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1

Heterogeneous nucleation of a monomer gas on a growing gas-phase polymer  

E-print Network

Heterogeneous nucleation of a monomer gas on a growing gas-phase polymer Chaok Seok and David W for gas-phase polymerization. We have used a density functional approach to calculate the free energy and heterogeneous nucleation rate of liquid drops of monomer on oligomer chains of varying length. We show

Seok, Chaok

2

THE NUCLEATION AND GROWTH OF GAS BUBBLES IN A NEWTONIAN FLUID: AN ENERGETIC VARIATIONAL PHASE  

E-print Network

THE NUCLEATION AND GROWTH OF GAS BUBBLES IN A NEWTONIAN FLUID: AN ENERGETIC VARIATIONAL PHASE FIELD and growth of gas bubbles in a Newtonian fluid. We employ a general energetic variational formulation with those of classical models. The new approach allows the study of bubble nucleation, growth

Feng, James J.

3

Nucleation of gas hydrates  

Microsoft Academic Search

The kinetics of nucleation of one-component gas hydrates in aqueous solutions are analyzed. The size of the hydrate nucleus and the work for nucleus formation are determined as functions of the supersaturation ??. Expressions for the stationary rate J of hydrate nucleation are derived. These expressions describe the J(??) dependence for homogeneous nucleation and for heterogeneous nucleation at the solution\\/gas

Dimo Kashchiev; Abbas Firoozabadi

2002-01-01

4

Nucleation of gas hydrates  

NASA Astrophysics Data System (ADS)

The kinetics of nucleation of one-component gas hydrates in aqueous solutions are analyzed. The size of the hydrate nucleus and the work for nucleus formation are determined as functions of the supersaturation ? ?. Expressions for the stationary rate J of hydrate nucleation are derived. These expressions describe the J(? ?) dependence for homogeneous nucleation and for heterogeneous nucleation at the solution/gas interface or on solid substrates and nucleation-active microparticles in the solution. The results are applied to nucleation of methane hydrate in solutions containing additives that may act as kinetic inhibitors of the process.

Kashchiev, Dimo; Firoozabadi, Abbas

2002-09-01

5

Numerical Analysis of an Impinging Jet Reactor for the CVD and Gas-Phase Nucleation of Titania  

NASA Technical Reports Server (NTRS)

We model a cold-wall atmospheric pressure impinging jet reactor to study the CVD and gas-phase nucleation of TiO2 from a titanium tetra-iso-propoxide (TTIP)/oxygen dilute source gas mixture in nitrogen. The mathematical model uses the computational code FIDAP and complements our recent asymptotic theory for high activation energy gas-phase reactions in thin chemically reacting sublayers. The numerical predictions highlight deviations from ideality in various regions inside the experimental reactor. Model predictions of deposition rates and the onset of gas-phase nucleation compare favorably with experiments. Although variable property effects on deposition rates are not significant (approximately 11 percent at 1000 K), the reduction rates due to Soret transport is substantial (approximately 75 percent at 1000 K).

Gokoglu, Suleyman A.; Stewart, Gregory D.; Collins, Joshua; Rosner, Daniel E.

1994-01-01

6

Modeling gas-phase nucleation in inductively coupled silane-oxygen S.-M. Suh, S. L. Girshick,a)  

E-print Network

Modeling gas-phase nucleation in inductively coupled silane-oxygen plasmas S.-M. Suh, S. L. An inductively coupled plasma reactor was modeled in a one-dimensional multicomponent two-temperature framework while also having the capability of anisotropic deep etching. Inductively coupled plasmas ICPs

Zachariah, Michael R.

7

Bubble nucleation from gas cavities — a review  

Microsoft Academic Search

This review is concerned with the nucleation of bubbles in solutions supersaturated with a gas, in particular the bubble nucleation that occurs at specific sites, as a cycle. A classification system for the kinds of nucleation that occur is defined and discussed in order to place this specific form of nucleation into a better defined context. It is noted that

S. F. Jones; G. M. Evans; K. P. Galvin

1999-01-01

8

Tungsten oxide nanoparticles synthesised by laser assisted homogeneous gas-phase nucleation  

Microsoft Academic Search

Tungsten oxide nanoparticles were generated by excimer (ArF) laser assisted chemical vapor deposition from WF6\\/H2\\/O2\\/Ar gas mixtures. The deposited particles were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, and transmission electron microscopy. The deposition rate as a function of the partial pressures of the reactants and of the laser fluence was measured by X-ray fluorescence spectroscopy. The mean diameter of

O. Alm; L. Landström; M. Boman; C. G. Granqvist; P. Heszler

2005-01-01

9

Homogeneous nucleation of diamond powder by CO2 -laser-driven gas-phase reactions  

Microsoft Academic Search

Diamond powders with grain diameters up to 0.3 ?m were obtained by CO2 -laser-induced decomposition of C2H4 at low pressures and temperatures. C2H4 or mixtures of C2H4, H2, and SiH4 were irradiated in a gas-flow reactor with the 10P14 line (10.532 ?m) of a grating-tunable CO2 laser with 50-W cw output power. Solid products were produced in a yellow-to-orange colored

Peter R. Buerki; Samuel Leutwyler

1991-01-01

10

Properties of the seismic nucleation phase  

USGS Publications Warehouse

Near-source observations show that earthquakes begin abruptly at the P-wave arrival, but that this beginning is weak, with a low moment rate relative to the rest of the main shock. We term this initial phase of low moment rate the seismic nucleation phase. We have observed the seismic nucleation phase for a set of 48 earthquakes ranging in magnitude from 1.1-8.1. The size and duration of the seismic nucleation phase scale with the total seismic moment of the earthquake, suggesting that the process responsible for the seismic nucleation phase carries information about the eventual size of the earthquake. The seismic nucleation phase is characteristically followed by quadratic growth in the moment rate, consistent with self-similar rupture at constant stress drop. In this paper we quantify the properties of the seismic nucleation phase and offer several possible explanations for it.

Beroza, G.C.; Ellsworth, W.L.

1996-01-01

11

Seismic evidence for an earthquake nucleation phase  

USGS Publications Warehouse

Near-source observations show that earthquakes initiate with a distinctive seismic nucleation phase that is characterized by a low rate of moment release relative to the rest of the event. This phase was observed for the 30 earthquakes having moment magnitudes 2.6 to 8.1, and the size and duration of this phase scale with the eventual size of the earthquake. During the nucleation phase, moment release was irregular and appears to have been confined to a limited region of the fault. It was characteristically followed by quadratic growth in the moment rate as rupture began to propagate away from the nucleation zone. These observations suggest that the nucleation process exerts a strong influence on the size of the eventual earthquake.

Ellsworth, W.L.; Beroza, G.C.

1995-01-01

12

Gas-liquid nucleation in nonideal molecular systems  

NASA Astrophysics Data System (ADS)

Nucleation is the initial step of a first order phase transition. In this thesis, some aspects of gas-liquid nucleation in systems of atmospheric importance are investigated. Nucleation is part of the gas-to-particle transition in the atmosphere. The gaseous pollutants released in the atmosphere due to human activities affect the transition processes an thus the size distribution and chemical properties of aerosol particles. Also the properties and appearance of clouds are affected. Aerosol particles and clouds have profound effects on e.g. the climate change, ozone depletion and acidification. Thermal collisions are generally used as a model of the nucleation process. Clusters are formed by kinetic collisions and their decay rates depend on their formation energies. If a cluster undergoes sufficient amount of collisions, it forms a droplet, which tends to grow further. In this study, kinetics of one- and two- component steady-state nucleation is investigated by solving the birth-death equations numerically. The validity of some of the commonly used approximations concerning nucleation kinetics are tested. The approximations are found to work well in most cases. The present theories fail in predicting the formation energies of small and non-ideal clusters. It is shown, that nucleation rates calculated with different models for the formation energy differ significantly in conditions corresponding to accidental ammonia release. Sulphuric acid-water mixture is considered to be one of the most important nucleating vapour systems in atmosphere. Sulphuric acid molecules are bound to hydrates, small clusters that contain a few water molecules. Hydrates play an important role in the nucleation process. To predict the formation energies of the hydrates, molecular-level effects have to be taken into account. The ab initio study of small sulphuric acid-water cluster included in the thesis is the first step towards understanding the properties of the hydrates.

Arstila, Hanna Tuula Katariina

13

Evolution of gas saturation and relative permeability during gas production from hydrate-bearing sediments: Gas invasion vs. gas nucleation  

NASA Astrophysics Data System (ADS)

and both gas and water permeabilities change as a function of gas saturation. Typical trends established in the discipline of unsaturated soil behavior are used when simulating gas production from hydrate-bearing sediments. However, the evolution of gas saturation and water drainage in gas invasion (i.e., classical soil behavior) and gas nucleation (i.e., gas production) is inherently different: micromodel experimental results show that gas invasion forms a continuous flow path while gas nucleation forms isolated gas clusters. Complementary simulations conducted using tube networks explore the implications of the two different desaturation processes. In spite of their distinct morphological differences in fluid displacement, numerical results show that the computed capillarity-saturation curves are very similar in gas invasion and nucleation (the gas-water interface confronts similar pore throat size distribution in both cases); the relative water permeability trends are similar (the mean free path for water flow is not affected by the topology of the gas phase); and the relative gas permeability is slightly lower in nucleation (delayed percolation of initially isolated gas-filled pores that do not contribute to gas conductivity). Models developed for unsaturated sediments can be used for reservoir simulation in the context of gas production from hydrate-bearing sediments, with minor adjustments to accommodate a lower gas invasion pressure Po and a higher gas percolation threshold.

Jang, Jaewon; Santamarina, J. Carlos

2014-01-01

14

Nucleation of Ordered Phases in Block Copolymers  

NASA Astrophysics Data System (ADS)

Nucleation of various ordered phases in block copolymers is studied by examining the free-energy landscape within the self-consistent field theory. The minimum energy path (MEP) connecting two ordered phases is computed using a recently developed string method. The shape, size, and free-energy barrier of critical nuclei are obtained from the MEP, providing information about the emergence of a stable ordered phase from a metastable phase. In particular, structural evolution of embryonic gyroid nucleus is predicted to follow two possible MEPs, revealing an interesting transition pathway with an intermediate perforated layered structure.

Cheng, Xiuyuan; Lin, Ling; E, Weinan; Zhang, Pingwen; Shi, An-Chang

2010-04-01

15

Homogeneous nucleation of droplets from a supersaturated vapor phase Michael P. Moody and Phil Attard  

E-print Network

Homogeneous nucleation of droplets from a supersaturated vapor phase Michael P. Moody and Phil the homogeneous nucleation of droplets from a supersaturated vapor, beginning with a partition function state with unfavorably high supersaturation levels being maintained in the gas phase. Homogeneous

Attard, Phil

16

Nucleation and growth of Nb nanoclusters during plasma gas condensation  

SciTech Connect

Niobium nanoclusters were produced using a plasma gas condensation process. The influence of gas flow rate, aggregation length, and source current on the nanocluster nucleation and growth were analyzed. Nanoclusters with an average diameter from 4 nm to 10 nm were produced. Cluster size and concentration were tuned by controlling the process inputs. The effects of each parameter on the nucleation zone, growth length, and residence time was examined. The parameters do not affect the cluster formation and growth independently; their influence on cluster formation can be either cumulative or competing. Examining the nucleation and growth over a wide combination of parameters provided insight into their interactions and the impact on the growth process. These results provide the opportunity for a broader understanding into the nucleation and growth of nanoclusters and some insights into how process parameters interact during deposition. This knowledge will enhance the ability to create nanoclusters with desired size dispersions.

Bray, K. R.; Jiao, C. Q. [UES, Inc., 4401 Dayton-Xenia Rd, Dayton, Ohio 45432 (United States)] [UES, Inc., 4401 Dayton-Xenia Rd, Dayton, Ohio 45432 (United States); DeCerbo, J. N. [Air Force Research Laboratory, AFRL/RQQE, 1950 Fifth St., WPAFB, Ohio 45433 (United States)] [Air Force Research Laboratory, AFRL/RQQE, 1950 Fifth St., WPAFB, Ohio 45433 (United States)

2013-06-21

17

Simulation and Kinetics of Grain-Boundary Nucleated Phase Transformations  

E-print Network

Simulation and Kinetics of Grain-Boundary Nucleated Phase Transformations E.A. Jägle1, E fields overlap e.g. Phase-Field simulations1 1 Bruna et al., J. Appl. Phys. 100 (2006) 054907 / 2 violated e.g. if diffusion fields overlap e.g. Phase-Field simulations1 equiaxed growth violated e

Cambridge, University of

18

Nucleation  

PubMed Central

Crystallization starts with nucleation and control of nucleation is crucial for the control of the number, size, perfection, polymorphism and other characteristics of crystalline materials. This is particularly true for crystallization in solution, which is an essential part of processes in the chemical and pharmaceutical industries and a major step in physiological and pathological phenomena. There have been significant recent advances in the understanding of the mechanism of nucleation of crystals in solution. The foremost of these are the two-step mechanism of nucleation and the notion of the solution–crystal spinodal. According to the two-step mechanism, the crystalline nucleus appears inside pre-existing metastable clusters of size several hundred nanometers, which consist of dense liquid and are suspended in the solution. While initially proposed for protein crystals, the applicability of this mechanism has been demonstrated for small molecule organic materials, colloids, polymers, and biominerals. This mechanism helps to explain several long-standing puzzles of crystal nucleation in solution: nucleation rates which are many orders of magnitude lower than theoretical predictions, the significance of the dense protein liquid, and others. At high supersaturations typical of most crystallizing systems, the generation of crystal embryos occurs in the spinodal regime, where the nucleation barrier is negligible. The solution-crystal spinodal helps to understand the role of heterogeneous substrates in nucleation and the selection of crystalline polymorphs. Importantly, these ideas provide powerful tools for control of the nucleation process by varying the solution thermodynamic parameters. PMID:21132117

Vekilov, Peter G.

2010-01-01

19

Investigation of metal and metal oxide clusters small enough to constitute the critical size for gas phase nucleation in combustion processes. Final report, 1 October 1975-30 June 1979  

SciTech Connect

Over the course of this contract a variety of techniques have been employed to study the properties of small atomic and molecular clusters formed in the gas phase via homogeneous nucleation. The clustering occurs either in an adiabatic expansion of a condensable species (e.g. argon, krypton, xenon, or sulfur hexafluoride) in an inert carrier gas (e.g. helium), or as a mixing process using a hot condensable (e.g. lead, silver, copper, indium or bismuth) and a cold carrier gas (e.g. argon, helium, carbon dioxide or sulfur hexafluoride). A continuous development several types of cluster sources has been carried out and includes free jets, very small hypersonic laval nozzles, and a series of metal ovens with carrier gas mixing. Any one, of these sources, constitutes the first stage of a differentially pumped, molecular beam system which the produces a continuous beam of clusters. The denisty in the beam is so low that it is collisionless and thus the clusters do not interact with each other or with any other foreign molecule or surface. The study of these isolated clusters is carried out primarily using high energy electron beams (40 to 75 KeV). The resulting diffraction patterns are obtained either on film or through use of a single channel, scintillation, pulse counting system employing synchronous detection.

Stein, G.D.

1980-11-01

20

Perturbed vortex lattices and the stability of nucleated topological phases  

NASA Astrophysics Data System (ADS)

We study the stability of nucleated topological phases that can emerge when interacting non-Abelian anyons form a regular array. The studies are carried out in the context of Kitaev's honeycomb model, where we consider three distinct types of perturbations in the presence of a lattice of Majorana mode binding vortices—spatial anisotropy of the vortices, dimerization of the vortex lattice, and local random disorder. While all the nucleated phases are stable with respect to weak perturbations of each kind, strong perturbations are found to result in very different behavior. Anisotropy of the vortices stabilizes the strong-pairing-like phases, while dimerization can recover the underlying non-Abelian phase. Local random disorder, on the other hand, can drive all the nucleated phases into a gapless thermal metal state. We show that all these distinct behaviors can be captured by an effective staggered tight-binding model for the Majorana modes. By studying the pairwise interactions between the vortices, i.e., the amplitudes for the Majorana modes to tunnel between vortex cores, the locations of phase transitions and the nature of the resulting states can be predicted. We also find that, due to oscillations in the Majorana tunneling amplitude, lattices of Majorana modes may exhibit a Peierls-like instability, where a dimerized configuration is favored over a uniform lattice. As the nature of the nucleated phases depends only on the Majorana tunneling, our results are expected to apply also to other system supporting localized Majorana mode arrays, such as Abrikosov lattices in p-wave superconductors, Wigner crystals in Moore-Read fractional quantum Hall states, or arrays of topological nanowires.

Lahtinen, Ville; Ludwig, Andreas W. W.; Trebst, Simon

2014-02-01

21

Nucleation of the diamond phase in aluminium-solid solutions  

NASA Technical Reports Server (NTRS)

Precipitation was studied from fcc solid solutions with silicon, germanium, copper and magnesium. Of all these elements only silicon and germanium form diamond cubic (DC) precipitates in fcc Al. Nucleation of the DC structure is enhanced if both types of atom are dissolved in the fcc lattice. This is interpreted as due to atomic size effects in the prenucleation stage. There are two modes of interference of fourth elements with nucleation of the DC phase in Al + Si, Ge. The formation of the DC phase is hardly affected if the atoms (for example, copper) are rejected from the (Si, Ge)-rich clusters. If additional types of atom are attracted by silicon and/or germanium, DC nuclei are replaced by intermetallic compounds (for example Mg2Si).

Hornbogen, E.; Mukhopadhyay, A. K.; Starke, E. A., Jr.

1993-01-01

22

Nucleation of a new phase on a surface that is changing irreversibly with time  

E-print Network

Nucleation of a new phase almost always starts at a surface. This surface is almost always assumed not to change with time. However, surfaces can roughen, partially dissolve and change chemically with time. Each of these irreversible changes will change the nucleation rate at the surface, resulting in a time-dependent nucleation rate. Here we use a simple model to show that partial surface dissolution can qualitatively change the nucleation process, in a way that is testable in experiment. The changing surface means that the nucleation rate is increasing with time. There is an initial period during which no nucleation occurs, followed by relatively rapid nucleation.

Richard P. Sear

2014-01-02

23

Electromagnetic emissions during seismic nucleation phase of stick-slips  

NASA Astrophysics Data System (ADS)

I. Introduction The size of seismic nucleation is determined by the characteristic wavelength of slip surface topography, and some scaling laws are derived from it (Ohnaka and Shen, 1999). Alternative characteristic wavelength should be introduced for natural faults because they are associated with layers of fault gouge. Riedel shear will be an equivalent since it is a characteristic structure inside fault zones. II. Method of stick- slip experiments Experimental apparatus: tri-axial apparatus. Samples: granite and gabbro cylinders of 20mmx40mm. Precut surface: 50 degree against sample axis and mirror-finished. Simulated fault gouge: quartz and gabbro powder of 0.25g. Sensors: strain gauges for measurements of axial stress and slip distance as well as three shear strain gauges pasted along a slip surface, three pairs of electrodes for measurement of triboelectric potentials. Data acquisition: continuously and synchronously at 2MHz. Experimental procedure: loading of axial stress after holding at confining pressure of 80-180 MPa and shear stress at 250 MPa during 0.1-1 hour for compaction of gouge. III. Experimental results 1) Stick-slips on bare surfaces Fluctuations of the electrode potentials during main stick-slip events are 55-180mV. Gabbro and granite samples do not show significant differences in magnitude of electrode potential. Any experimental runs were not associated with nucleation phases. Prior to main stick-slip events spike-like signals of electrode potentials were sometimes found synchronously with very small stress drops less than 1MPa. The amplitudes are less than 30mV, and they decayed exponentially. 2) Stick-slips with fault gouge Stress drops and fluctuations of electrode potentials at main stick-slip events are 7-400 MPa, 17-200mV+. Significant differences in fluctuations of electrode potentials were not found between granite and gabbro samples. About 30% of all experimental runs were associated with a nucleation phase. Slip distance, stress drop, duration and the maximum fluctuation of electrode potentials were 0.02mm, 14MPa, 0.3sec and 20mV in an experimental run, and the latter three were 3.5MPa, 0.35sec and 4mV in another run. Three pairs of strain gauges recorded the initial site and its propagation of a seismic nucleation. The potentials of three pairs of electrodes also fluctuated synchronously. The pulse-like electrode signals were sometimes found also for these experiments. IV. Discussions and conclusions 1) The reason why the stick-slips on bare surfaces were not associated with a nucleation phase is attributed to mirror-finished smooth and flat precut surfaces. 2) Irrespective of granite or gabbro powders of fault gouge, there were not significant differences in magnitude of pulse-like fluctuations of electrode potentials. This is the case for main stick-slip events. These indicate that the causes of the electric signals are not piezoelectric effect but triboelectricity and/or fracto-emission. 3) Since the fluctuations of electrode potentials are synchronous with the initiation and propagation of a nucleation, the former is attributed to the latter. 4) It is very likely that nucleation is quasi-static slip on a Riedel shear because the length of a nuclei estimated from slip during nucleation phases is the same order as the length of Riedel shears.

Onuma, K.; Otsuki, K.

2008-12-01

24

Control of protein crystal nucleation around the metastable liquidliquid phase boundary  

E-print Network

Control of protein crystal nucleation around the metastable liquid­liquid phase boundary Oleg to enhance or suppress the nucleation of protein crystals opens opportunities in various fundamental and applied areas, including protein crystallography, production of protein crystalline pharmaceuticals

Vekilov, Peter

25

Homogeneous nucleation of particles from the vapor phase in thermal plasma synthesis  

Microsoft Academic Search

Particle nucleation and growth are simulated for iron vapor in a thermal plasma reactor with an assumed one-dimensional flow field and decoupled chemistry and aerosol dynamics. Including both evaporation and coagulation terms in the set of cluster-balance rate equations, a sharply defined homogeneous nucleation event is calculated. Following nucleation the vapor phase is rapidly depleted by condensation, and thereafter particle

S. L. Girshick; C.-P. Chiu

1989-01-01

26

Heat storage system comprising a phase change medium and a nucleating agent  

SciTech Connect

A heat storage system comprises a phase change medium and a nucleating agent. The phase change medium is prepared by mixing a gest molecule and water if necessary, with a gelating agent, an emulsifier and/or a furan compound. The nucleating agent is filled in a capillary or a porous substrate.

Kai, J.; Kimura, H.

1982-06-01

27

Thermodynamics and Kinetics of Nanoclusters Controlling Gas-to-Particle Nucleation  

Microsoft Academic Search

Nucleation of new particles from vapor-phase molecular precursors is an important process in the synthesis of nanomaterials and in the formation of aerosols in the atmosphere. Vapor-to-particle nucleation is a macroscopic process controlled by nanoscale particles (e.g., molecular clusters). Computational approaches to nucleation have been limited by the lack of a consistent theory of the process and by the lack

Shawn M. Kathmann; Gregory K. Schenter; Bruce C. Garrett; Bin Chen; J. Ilja Siepmann

2009-01-01

28

Effect of Molecular Rotation on Vapor Phase Nucleation: Fullerenes C60 and C70  

Microsoft Academic Search

The effect of rotational free energy of fullerenes C60 and C70 on homogeneous nucleation of crystals from vapor phase have been studied. Classical nucleation parameters have been estimated for the case of nucleation and crystal growth of C60 and C70 by Physical Vapor Transport (PVT) method under different supercooling in the range of 20–150 K, keeping the source temperatures constant.

C. Sekar; R. Dhanasekaran; C. Subramanian

1996-01-01

29

Phase-field simulation of microstructure development involving nucleation and crystallographic orientations in alloy solidification  

NASA Astrophysics Data System (ADS)

A proper treatment of nucleation in phase-field simulations is developed, in which the calculation of nucleation kinetics in binary melts is taken into account and the free energy change of nucleation is obtained by maximizing it relative to the composition of the nuclei. Using the phase-field model for polycrystalline solidification coupled with the nucleation strategy, the typical solidification microstructures encountered in castings are simulated. The selection of columnar grains and the columnar-to-equiaxed transition (CET) are clearly shown. The results also indicate that the columnar zone length and the equiaxed grain size increase with a decrease in cooling rate, which results from the competition between nucleation and growth.

Li, Junjie; Wang, Jincheng; Yang, Gencang

2007-11-01

30

Journal of Crystal Growth 243 (2002) 476489 Nucleation of gas hydrates  

E-print Network

Journal of Crystal Growth 243 (2002) 476­489 Nucleation of gas hydrates Dimo Kashchieva , Abbas the process of crystallization of gas hydrates. At the same time, its understanding could be the key to the kinetic inhibition or promotion of this process. The kinetics of gas hydrate crystallization are covered

Firoozabadi, Abbas

31

Thermodynamics and Kinetics of Nanoclusters Controlling Gas-to-Particle Nucleation  

SciTech Connect

Nucleation of new particles from vapor-phase molecular precursors is an important process in the synthesis of nanomaterials and in the formation of aerosols in the atmosphere. Vapor-to-particle nucleation is a macroscopic process controlled by nanoscale particles (e.g., molecular clusters). Computational approaches to nucleation have been limited by the lack of a consistent theory of the process and by the lack of efficient approaches to simulate the properties of clusters relevant to nucleation. In this article, we focus on two advances that allow nucleation to be treated in a rigorous manner for molecular systems: Dynamical Nucleation Theory permits a consistent treatment of the nucleation kinetics and aggregation-volume-bias Monte Carlo simulations using self-adaptive umbrella sampling combined with histogram reweighting provides an efficient approach to evaluate the thermodynamics of molecular clusters important in nucleation. The combination of these two approaches positions molecular computational approaches to make significant advances in our understanding of the mechanisms of nucleation, particularly in multiple component systems that play crucial roles in nanoscience applications and in the atmosphere. This work was supported by the U.S. Department of Energy's (DOE) Office of Basic Energy Sciences, Chemical Sciences program. The Pacific Northwest National Laboratory is operated by Battelle for DOE.

Kathmann, Shawn M.; Schenter, Gregory K.; Garrett, Bruce C.; Chen, Bin; Siepmann, J. I.

2009-06-18

32

Nucleation and growth of the normal phase in thin superconducting strips  

SciTech Connect

We investigated the kinetics of normal phase nucleation and flux line condensation in the type-II superconductors by numerical study of the time-dependent Ginzburg-Landau equation. We have shown that under a sufficient transport current the normal phase nucleates in superconducting strips in the form of the macroscopic droplets having multiple topological charge. We discussed the stability and dynamics of the droplets. We have found that pinning suppresses the droplet formation. {copyright} {ital 1995 The American Physical Society.}

Aranson, I.; Shapiro, B.Y.; Vinokur, V. [Department of Physics and Jack and Pearl Resnick Institute of Advanced Technology, Bar Ilan University, Ramat Gan 52900 (Israel)] [Department of Physics and Jack and Pearl Resnick Institute of Advanced Technology, Bar Ilan University, Ramat Gan 52900 (Israel); [Argonne National Laboratory, 9700 South Cass Avenue, Argonne, Illinois 60439 (United States)

1996-01-01

33

Nucleation of atmospheric aerosol particles  

NASA Astrophysics Data System (ADS)

A significant fraction of the total number of particles present in the atmosphere is formed originally by nucleation from the gas phase. Binary nucleation of sulphuric acid and water, ternary nucleation of sulphuric acid, water and ammonia and ion-induced nucleation are thought to be the most important aerosol nucleation processes in the atmosphere. Within the last two decades, instrumentation to observe and characterize nucleation has improved greatly and numerous observations of nucleation have been made including quantification of the nucleation rate, characterization of the growth process and first chemical characterizations of the freshly formed particles. Nucleation has been observed at many different places in the atmosphere: in the boundary layer, in the free troposphere, in remote locations, in coastal areas, in boreal forests as well as urban areas and pollution plumes. In most cases gaseous sulphuric acid is assumed to be the key precursor gas. After nucleation, other supersaturated substances, especially low vapour pressure organics often take part in the subsequent aerosol growth. Iodine oxides seem to be responsible for nucleation observed in some coastal areas. Recent advances in modelling allow for a kinetic treatment of the nucleation process based on measured thermochemical data for the cluster formation. Considerable improvement over the classical nucleation treatment is expected from this approach. A detailed understanding of atmospheric aerosol nucleation processes is needed as the freshly formed particles directly influence the number concentration and size distribution of the atmospheric aerosol. The formation of clouds and precipitation is affected and influences on climate are anticipated. Anthropogenic emissions influence atmospheric aerosol nucleation processes considerably. Despite the comprehensive research efforts, substantial inconsistencies remain and conflicting results of laboratory studies, model studies as well as atmospheric observations persist. Several key questions about the predictability of atmospheric nucleation in general, about the substances, that take part in nucleation and subsequent growth and about the size and composition of the critical cluster, have not been resolved so far. To cite this article: J. Curtius, C. R. Physique 7 (2006).

Curtius, Joachim

2006-11-01

34

Molecular-dynamics simulation of homogeneous nucleation in the vapor phase  

Microsoft Academic Search

Ten independent quenches of a gas of 40 000 Lennard-Jones particles are followed until the systems exhibit droplet growth. The cluster distributions and the kinetics are determined for the quenched quasi-equilibrium state, at the onset of nucleation and at droplet growth. All the distributions are isomorphic with the particle distribution in the equilibrium gas state and asymptotically given by simple

S. Toxvaerd

2001-01-01

35

Localized orientational order chaperons the nucleation of Rotator phases in hard polyhedral particles  

E-print Network

The nucleation kinetics of the rotator phase in hard cuboctahedra, truncated octahedra, and rhombic dodecahedra is simulated via a combination of Forward Flux Sampling and Umbrella Sampling. For comparable degree of supersaturation, the polyhedra are found to have significantly lower free-energy barriers and faster nucleation rates than hard spheres. This difference primarily stems from localized orientational ordering, which steers polyhedral particles to pack more efficiently. Orientational order hence fosters here the growth of orientationally disordered nuclei.

Vikram Thapar; Fernando A. Escobedo

2013-11-11

36

Role of nucleation and growth in two-phase microstructure formation  

NASA Astrophysics Data System (ADS)

During the directional solidification of peritectic alloys, a rich variety of two-phase microstructures develop, and the selection process of a specific microstructure is complicated due to the following two considerations. (1) In contrast to many single phase and eutectic microstructures that grow under steady state conditions, two-phase microstructures in a peritectic system often evolve under non-steady-state conditions that can lead to oscillatory microstructures, and (2) the microstructure is often governed by both the nucleation and the competitive growth of the two phases in which repeated nucleation can occur due to the change in the local conditions during growth. In this research, experimental studies in the Sn-Cd system were designed to isolate the effects of nucleation and competitive growth on the dynamics of complex microstructure formation. Experiments were carried out in capillary samples to obtain diffusive growth conditions so that the results can be analyzed quantitatively. At high thermal gradient and low velocity, oscillatory microstructures were observed in which repeated nucleation of the two phases was observed at the wall-solid-liquid junction. Quantitative measurements of nucleation undercooling were obtained for both the primary and the peritectic phase nucleation, and three different ampoule materials were used to examine the effect of different contact angles at the wall on nucleation undercooling. Nucleation undercooling for each phase was found to be very small, and the experimental undercooling values were orders of magnitude smaller than that predicted by the classical theory of nucleation. A new nucleation mechanism is proposed in which the clusters of atoms at the wall ahead of the interface can become a critical nucleus when the cluster encounters the triple junction. Once the nucleation of a new phase occurs, the microstructure is found to be controlled by the relative growth of the two phases that give rise to different oscillatory microstructures that depend on the imposed velocity and the size of the sample. At low thermal gradient to velocity ratio, a steady-state composite microstructure is observed. Two mechanisms of composite microstructure formation were examined: (i) the formation of the peritectic phase in the intercellular region of the primary phase where the solute rejected by the primary phase is absorbed by the peritectic phase. The peritectic phase forms a small distance behind the growing primary phase front. (ii) The second mechanism is the coupled growth of the two phases with a macroscopically planar interface, as in the case of eutectic growth. Detailed studies showed that this composite microstructure, although it appears as a eutectic microstructure, did not grow in the coupled manner at the advancing interface in the Sn-Cd system. However, a new observation was made when experiments were carried out in thin ampoule of Ta. The peritectic phase nucleated at the wall-interface triple junction and grew along the wall, while the primary phase continued to grow at the center, giving rise to a steady-state couple growth at some specific velocity. The mechanism of coupled growth in this case was shown to be operative due to the presence of a finite contact angle at the wall, and this was demonstrated by including the contact angle effect at the wall in the rod eutectic growth model. The experimental results were summarized to map out the conditions of thermal gradient and velocity on the regimes of composite and oscillatory microstructure formation. The formation of complex time-dependent microstructures was then discussed in terms of the time-dependent dynamics of planar interface growth.

Shin, Jong Ho

37

Interplay between ?(Ti) nucleation and growth during peritectic solidification investigated by phase-field simulations.  

PubMed

The properties of modern TiAl-based alloys with aluminum contents around 45 at.% critically depend on the as solidified ?(Ti) grain structure. Commonly, a rather coarse grain structure is obtained if ?(Ti) forms via the peritectic reaction '[Formula: see text]'. Phase-field simulations have been applied to perform a case study of grain structure formation during the early peritectic growth under unidirectional growth conditions. In the absence of foreign nucleation sites, the peritectic ?(Ti) phase nucleates on the dendritic surface of the properitectic ?(Ti) phase. For typical values of the critical nucleation undercooling, coarse structures with large elongated grains are reproduced. A delicate interplay between nucleation and growth is predicted for reduced values of the critical undercooling. In this case, the alloy composition is found to play an additional role. An effective grain refinement by frequent nucleation is obtained, if potent nucleants can reduce the critical undercooling below the local growth undercooling. Complementary Scheil calculations and Bridgman experiments show that in situ precipitation of TiB(2) particles can be controlled by adequate boron addition. Both, numerical predictions and experiments confirm that these particles can act as effective nucleation agents and significantly reduce the grain size of ?(Ti). PMID:21715868

Eiken, J; Apel, M; Witusiewicz, V T; Zollinger, J; Hecht, U

2009-11-18

38

Exploring the discrepancies between experiment, theory, and simulation for the homogeneous gas-to-liquid nucleation of 1-pentanol  

NASA Astrophysics Data System (ADS)

Using an efficient Monte Carlo approach known as Aggregation-Volume-bias Monte Carlo with self-adaptive Umbrella Sampling and Histogram Reweighting (AVUS-HR), we obtained the nucleation free energy profile of 1-pentanol at various temperatures from 220 to 360 K. From these profiles, differences between the free energy barrier heights obtained from our simulations and those predicted by the classical nucleation theory (CNT) were calculated. Our results strongly support that the logarithm of the nucleation rate ratio between simulation (or experiment) and CNT increases almost linearly with the inverse temperature. Among the various factors that contribute to the discrepancy between simulation and CNT nucleation rates, the nonzero surface free energy of the monomer included in the CNT makes the largest contribution. On the molecular level, the simulations indicate that a gas-phase cluster of 1-pentanol molecules is relatively compact and can contain multiple hydrogen bonded aggregates of various sizes and that this aggregate size distribution depends strongly on temperature and also on the overall size of the cluster system.

Nellas, Ricky B.; Keasler, Samuel J.; Siepmann, J. Ilja; Chen, Bin

2010-04-01

39

Phase field theory of interfaces and crystal nucleation in a eutectic system of fcc structure: II. Nucleation in the metastable liquid immiscibility region.  

PubMed

In the second part of our paper, we address crystal nucleation in the metastable liquid miscibility region of eutectic systems that is always present, though experimentally often inaccessible. While this situation resembles the one seen in single component crystal nucleation in the presence of a metastable vapor-liquid critical point addressed in previous works, it is more complex because of the fact that here two crystal phases of significantly different compositions may nucleate. Accordingly, at a fixed temperature below the critical point, six different types of nuclei may form: two liquid-liquid nuclei: two solid-liquid nuclei; and two types of composite nuclei, in which the crystalline core has a liquid "skirt," whose composition falls in between the compositions of the solid and the initial liquid phases, in addition to nuclei with concentric alternating composition shells of prohibitively high free energy. We discuss crystalline phase selection via exploring/identifying the possible pathways for crystal nucleation. PMID:17718630

Tóth, Gyula I; Gránásy, László

2007-08-21

40

Investigating heterogeneous nucleation in peritectic materials via the phase-field method  

Microsoft Academic Search

Here we propose a phase-field approach to investigate the influence of convection on peritectic growth as well as the heterogeneous nucleation kinetics of peritectic systems. For this purpose we derive a phase-field model for peritectic growth taking into account fluid flow in the melt, which is convergent to the underlying sharp interface problem in the thin interface limit (Karma and

Heike Emmerich; Ricardo Siquieri

2006-01-01

41

The influence of additives and metal rods on the nucleation and growth of gas hydrates.  

PubMed

A major technical issue in industrial applications of the gas hydrate storage process is to develop a practical means for rapid hydrate formation. In this paper, the formation processes of HCFC141b (CH(3)CCl(2)F) gas hydrate in a column of water with additives and with an iron rod that was placed in the center of the column have been studied to reveal the influence of the additives and the iron rod on the nucleation and growth of the gas hydrate. The water solution column, in a cylindrical glass container, was placed in a thermostatic bath at 274.15-280.15 K and under atmospheric pressure. The experimental results show that, compared to the pure water and the HCFC141b system, the properly placed iron rod combined with proper concentrations of lauryl sodium sulfonate, lauryl sodium sulfate, and sodium dodecylbenzenesulfonate-6 considerably reduces the hydrate nucleation time and promotes formation speed. The formation rate of HCFC141b gas hydrate increases with increasing concentration of sodium dodecylbenzenesulfonate-6 in the water solution, while the addition of potassium oxalate monohydrate in water has shown no effect on the nucleation and growth of HCFC141b gas hydrate. Under the experimental conditions, both the anion surfactants and the iron rod strongly induce the first nucleation of HCFC141b gas hydrate, while the following growth of the HCFC141b gas hydrate is primarily influenced by the anion surfactant. This experiment suggests a new way of fast formation of clathrate hydrate, which may be much easier for practical application of the gas hydrate for cold storage in air conditioning systems. PMID:15694442

Li, Jinping; Liang, Deqing; Guo, Kaihua; Wang, Ruzhu

2005-03-01

42

Nucleation-Suppressed Phase Stabilization in Fe–Au Nanoparticles  

SciTech Connect

Four nanoparticle compositions, Fe–21, 35, 47, and 67 at. % Au, have been prepared to study the phase stability and solid-state transformation in confined Fe–Au nanoalloys. The formation of two phases, predicted from bulk thermodynamics, has been suppressed in all compositions. Instead, a single phase solid solution forms after heat treatment at 600 °C and slow cooling. However, bulk phase relationships, signified by the precipitation of ?-Fe upon cooling, was observed in larger particles (>20 nm) with composition Fe–35 at. % Au. The suppression of the phase transformation/precipitation in small particles is explained thermodynamically, as the free energy decrease associated with the phase transformation does not exceed the increase in energy due to the introduction of an interphase interface (grain boundary) within the cluster. A general equation has been derived to predict the critical cluster size below which transformations are inhibited, which agrees well with the observed experimental results.

Mukherjee, P. [University of Nebraska; Jiang, Xiujuan [University of Nebraska; Wu, Yaqiao [Ames Laboratory; Kramer, Matthew J. [Ames Laboratory; Shield, J. E. [University of Nebraska

2013-10-18

43

Nucleation of Ti-catalyzed self-assembled kinked Si nanowires grown by gas source MBE  

NASA Astrophysics Data System (ADS)

Silicon nanowires catalyzed by Ti islands have been grown by molecular beam epitaxy using Si 2H 6 as the gas source and characterized by scanning electron microscopy, transmission electron microscopy, and in situ reflection high-energy electron diffraction. Two types of TiSi 2 islands, one with a flat top and the other with a dome-shaped top, are formed after Ti is deposited on a Si (0 0 1) wafer and subsequently annealed. Only dome-like islands nucleate Si nanowires if the Ti deposition temperature is below 850°C. Some of the flat-top islands also nucleate Si nanowires if Ti is deposited at 930°C. The reason for the nucleation at the higher temperature is that the two types of islands have different orientation and the high deposition temperature may change the orientation of the flat-top islands. Most of the grown Si nanowires are kinked because of twinning.

Tang, Qiang; Liu, Xian; Kamins, Theodore I.; Solomon, Glenn S.; Harris, James S.

2003-04-01

44

Tetragonal Lysozyme Nucleation and Crystal Growth: The Role of the Solution Phase  

NASA Technical Reports Server (NTRS)

Experimental evidence indicates a dominant role of solution phase interactions in nucleating and growing tetragonal lysozyme crystals. These interactions are extensive, even at saturation, and may be a primary cause of misoriented regions in crystals grown on Earth. Microgravity, by limiting interfacial concentrations to diffusion-controlled levels, may benefit crystal quality by also reducing the extent of associated species present at the interface.

Pusey, Marc L.; Forsythe, Elizabeth; Sumida, John; Maxwell, Daniel; Gorti, Sridhar; Curreri, Peter A. (Technical Monitor)

2002-01-01

45

Observation of the seismic nucleation phase in the Ridgecrest, California, earthquake sequence  

USGS Publications Warehouse

Near-source observations of five M 3.8-5.2 earthquakes near Ridgecrest, California are consistent with the presence of a seismic nucleation phase. These earthquakes start abruptly, but then slow or stop before rapidly growing again toward their maximum rate of moment release. Deconvolution of instrument and path effects by empirical Green's functions demonstrates that the initial complexity at the start of the earthquake is a source effect. The rapid growth of the P-wave arrival at the start of the seismic nucleation phase supports the conclusion of Mori and Kanamori [1996] that these earthquakes begin without a magnitude-scaled slow initial phase of the type observed by Iio [1992, 1995].

Ellsworth, W.L.; Beroza, G.C.

1998-01-01

46

A numerical method for the study of nucleation of ordered phases  

NASA Astrophysics Data System (ADS)

A numerical approach based on the string method is developed to study nucleation of ordered phases in first-order phase transitions. Among other things, this method allows an efficient computation of the minimum energy path (MEP) during the nucleation process. The MEP provides information about the size, shape and free energy barrier of the critical nucleus. To improve the efficiency of the string method, a special initialization process is proposed. Constraints from physical models are treated using two methods, a generalized coordinates method and a projection method. Strategies for choosing the computational domain and defining the nucleus boundary are also introduced. The validity of our approach is illustrated by two nontrivial examples from soft condensed matter physics, namely the nematic-isotropic transition of liquid crystals and the ordered-to-ordered phase transition of diblock copolymers.

Lin, Ling; Cheng, Xiuyuan; E, Weinan; Shi, An-Chang; Zhang, Pingwen

2010-03-01

47

Quantized hard-x-ray phase vortices nucleated by aberrated nanolenses  

SciTech Connect

Quantized x-ray phase vortices, namely, screw-type topological defects in the wave fronts of a coherent monochromatic scalar x-ray wave field, may be spontaneously nucleated by x-ray lenses. Phase retrieval is used to reconstruct the phase and amplitude of the complex disturbance created by aberrated gold nanolenses illuminated with hard x rays. A nanoscale quantized x-ray vortex-antivortex dipole is observed, manifest both as a pair of opposite-helicity branch points in the Riemann sheets of the multivalued x-ray phase map of the complex x-ray field and in the vorticity of the associated Poynting vector field.

Pavlov, Konstantin M. [School of Science and Technology, University of New England, Armidale, New South Wales 2351 (Australia); School of Physics, Monash University, Victoria 3800 (Australia); Paganin, David M. [School of Physics, Monash University, Victoria 3800 (Australia); Vine, David J. [ARC Centre of Excellence for Coherent X-ray Science, School of Physics, The University of Melbourne, Parkville, Victoria 3010 (Australia); Schmalz, Jelena A. [School of Science and Technology, University of New England, Armidale, New South Wales 2351 (Australia); Suzuki, Yoshio; Uesugi, Kentaro; Takeuchi, Akihisa; Yagi, Naoto [SPring-8/JASRI (Japan Synchrotron Radiation Research Institute), Hyogo 679-5198 (Japan); Kharchenko, Alexander; Blaj, Gabriel [PANalytical B.V., P.O. Box 13, 7600 AA Almelo (Netherlands); Jakubek, Jan [Institute of Experimental and Applied Physics, Czech Technical University in Prague, 166 36 Prague 6 (Czech Republic); Altissimo, Matteo [Melbourne Centre for Nanofabrication, 151 Wellington Road, Clayton, Victoria 3168 (Australia); Materials Science and Engineering, Commonwealth Scientific and Industrial Research Organisation, Clayton South, Victoria 3169 (Australia); Clark, Jesse N. [London Centre for Nanotechnology, University College, Gower St, London WC1E 6BT (United Kingdom)

2011-01-15

48

Numerical Analysis of Bubble Nucleation Processes for First-Order Phase Transitions Within Quantum Fields  

NASA Astrophysics Data System (ADS)

The well established links between statistical mechanics and quantum field theory have resulted in the extension of the theory of phase transitions to quantum fields. Within this framework first-order phase transition rates for quantum fields have traditionally been calculated via the Coleman "thin-wall" approximation. This approximation scheme is claimed to have validity in the situation where a first-order phase transition takes place between two nearly degenerate vacuum (ground) states. It is the purpose of this dissertation to make a comprehensive study of the range of validity of the "thin -wall" approximation via a comparison of its results with exact results obtained numerically. It is found that both in the absence of gravity and the presence of gravity the "thin-wall" approximation has a very restricted range of validity, and that it characteristically overestimates the phase transition rate. A new approximation scheme is presented which considerably improves upon the original "thin-wall" approximation, yet requires roughly the same degree of calculation effort as the original "thin-wall" approximation. The numerical analysis of first-order phase transitions within quantum fields is also extended to regimes not applicable to the "thin-wall" approximation in a search for new physical effects. An evolution from the "thin-wall" tunneling mode to the Hawking-Moss tunneling mode is observed for the decay from a de Sitter spacetime to a Minkowski spacetime. For the decay from Minkowski spacetime to an anti-de Sitter spacetime, the "thin-wall" approximation is seen to over -estimate the size of the "forbidden region" (predicted within the "thin-wall" approximation) in which the transition is not allowed. The effect of gravitationally compact objects upon vacuum phase transitions is considered within a perturbative analysis. It is found that they may act as nucleation sites for first-order phase transitions. The nucleation rate is maximized when the size of the gravitationally compact object is comparable to the size of the nucleating bubble associated with the phase transition. Some astrophysical applications of first-order vacuum phase transitions are analyzed. In particular, the post-nucleation evolution of a bubble of "new" phase; together with a relationship between the number density of possible astrophysical nucleation sites within the Universe (e.g., microscopic black-holes) and the mass of fermions within the Standard Model.

Samuel, David Adrian

49

Nucleation of (He-3)-B from the A phase - A cosmic-ray effect?  

NASA Technical Reports Server (NTRS)

When He-3 is liquified and subsequently cooled, it undergoes, at a temperature of approximately 2.0-2.5 mK, a second-order transition into the so-called A phase. On further cooling, a first-order transition occurs, and the liquid passes into the B phase. Supercooling occurs with respect to the second transition, and the problem of nucleation arises. In connection with the experimental interest in studying metastable (He-3)-A down to the lowest temperatures in weak magnetic fields, the understanding of the mechanism of this transition and the feasibility of its inhibition is of some importance. The present investigation is concerned with the possibility that the transition is nucleated by the passage of a cosmic ray through the sample cell.

Leggett, A. J.

1984-01-01

50

Gas-phase chemical dynamics  

SciTech Connect

Research in this program is directed towards the spectroscopy of small free radicals and reactive molecules and the state-to-state dynamics of gas phase collision, energy transfer, and photodissociation phenomena. Work on several systems is summarized here.

Weston, R.E. Jr.; Sears, T.J.; Preses, J.M. [Brookhaven National Laboratory, Upton, NY (United States)

1993-12-01

51

Gas Phase Anodization of Tantalum.  

National Technical Information Service (NTIS)

The anodic oxidation of tantalum in the gas phase was studied using an electromagnetic ion cathode. The anodic films were prepared at constant current densities of 1.0 and 2.0 ma/sq cm. The growth characteristics of anodic tantalum oxide films, in the gas...

T. A. Jennings, W. McNeill, R. E. Salomon

1967-01-01

52

Heterogeneous ice nucleation on phase-separated organic-sulfate particles: effect of liquid vs. glassy coatings  

NASA Astrophysics Data System (ADS)

Atmospheric ice nucleation on aerosol particles relevant to cirrus clouds remains one of the least understood processes in the atmosphere. Upper tropospheric aerosols as well as sub-visible cirrus residues are known to be enhanced in both sulfates and organics. The hygroscopic phase transitions of organic-sulfate particles can have an impact on both the cirrus cloud formation mechanism and resulting cloud microphysical properties. In addition to deliquescence and efflorescence, organic-sulfate particles are known to undergo another phase transition known as liquid-liquid phase separation. The ice nucleation properties of particles that have undergone liquid-liquid phase separation are unknown. Here, Raman microscopy coupled with an environmental cell was used to study the low temperature deliquescence, efflorescence, and liquid-liquid phase separation behavior of 2:1 mixtures of organic polyols (1,2,6-hexanetriol, and 1:1 1,2,6-hexanetriol +2,2,6,6-tetrakis(hydroxymethyl)cycohexanol) and ammonium sulfate from 240-265 K. Further, the ice nucleation efficiency of these organic-sulfate systems after liquid-liquid phase separation and efflorescence was investigated from 210-235 K. Raman mapping and volume-geometry analysis indicates that these particles contain solid ammonium sulfate cores fully engulfed in organic shells. For the ice nucleation experiments, we find that if the organic coatings are liquid, water vapor diffuses through the shell and ice nucleates on the ammonium sulfate core. In this case, the coatings minimally affect the ice nucleation efficiency of ammonium sulfate. In contrast, if the coatings become semi-solid or glassy, ice instead nucleates on the organic shell. Consistent with recent findings that glasses can be efficient ice nuclei, the phase separated particles are nearly as efficient at ice nucleation as pure crystalline ammonium sulfate.

Schill, G. P.; Tolbert, M. A.

2012-12-01

53

Heterogeneous ice nucleation on phase-separated organic-sulfate particles: effect of liquid vs. glassy coatings  

NASA Astrophysics Data System (ADS)

Atmospheric ice nucleation on aerosol particles relevant to cirrus clouds remains one of the least understood processes in the atmosphere. Upper tropospheric aerosols as well as sub-visible cirrus residues are known to be enhanced in both sulfates and organics. The hygroscopic phase transitions of organic-sulfate particles can have an impact on both the cirrus cloud formation mechanism and resulting cloud microphysical properties. In addition to deliquescence and efflorescence, organic-sulfate particles are known to undergo another phase transition known as liquid-liquid phase separation. The ice nucleation properties of particles that have undergone liquid-liquid phase separation are unknown. Here, Raman microscopy coupled with an environmental cell was used to study the low temperature deliquescence, efflorescence, and liquid-liquid phase separation behavior of 2 : 1 mixtures of organic polyols (1,2,6-hexanetriol and 1 : 1 1,2,6-hexanetriol + 2,2,6,6-tetrakis(hydroxymethyl)cyclohexanol) and ammonium sulfate from 240-265 K. Further, the ice nucleation efficiency of these organic-sulfate systems after liquid-liquid phase separation and efflorescence was investigated from 210-235 K. Raman mapping and volume-geometry analysis indicate that these particles contain solid ammonium sulfate cores fully engulfed in organic shells. For the ice nucleation experiments, we find that if the organic coatings are liquid, water vapor diffuses through the shell and ice nucleates on the ammonium sulfate core. In this case, the coatings minimally affect the ice nucleation efficiency of ammonium sulfate. In contrast, if the coatings become semi-solid or glassy, ice instead nucleates on the organic shell. Consistent with recent findings that glasses can be efficient ice nuclei, the phase-separated particles are nearly as efficient at ice nucleation as pure crystalline ammonium sulfate.

Schill, G. P.; Tolbert, M. A.

2013-05-01

54

Equations for nucleation of hydrogen gas pores during solidification of aluminium seven weight percent silicon alloy  

SciTech Connect

Producing metallic parts for aerospace and automotive industries in as-cast shapes is both less expensive and faster than many competitive manufacturing techniques. However, the occurrence of casting defects such as porosity limits the use of cast parts especially in high tolerance applications. In this work an empirical approach is followed to produce useable equations that reproduce the behavior of the material and which may then and in predicting the formation of gas porosity within solidification models. The approach of Charbon and Rappaz for grain nucleation during solidification is used to provide the form of the equations. Some possible explanations of the observed behavior are also presented.

Atwood, R.C.; Sridhar, S.; Lee, P.D.

1999-11-19

55

Ion-induced nucleation in polar one-component fluids Hikaru Kitamuraa  

E-print Network

Ion-induced nucleation in polar one-component fluids Hikaru Kitamuraa and Akira Onuki Department-Landau theory of ion-induced nucleation in polar one-component flu- ids in a gas phase. It will be based on our; published online 27 September 2005 We present a Ginzburg-Landau theory of ion-induced nucleation in a gas

56

Numerical Simulation on Hydrodynamics and Phase Change Associated with Multi-bubbles During Nucleate Boiling  

NASA Astrophysics Data System (ADS)

Development of predictive capability for hydrodynamics and phase change associated with multi-bubbles during nucleate boiling is essential to evaluate liquid wall protection schemes for various fusion chambers. This paper presents a numerical methodology for multiphase flow with phase change to help resolve feasibility issues encountered in the aforementioned fusion engineering fields. The numerical methodology is being conducted within the frame work of the incompressible flow with phase change. We present a new second order projection method, in conjunction with Approximate-Factorization techniques (AF method), for incompressible Navier-Stokes equations. The Crank-Nicholson method was used for the diffusion term to eliminate the numerical viscous stability restriction and 3rd order ENO scheme used for the convective term to guarantee the accuracy of the method. A four-level V cycle multigrid algorithm for pressure Poisson equation is used in order to decrease computation time. The level set method is used to capture the free surface of the flow and the deformation of the droplets accurately. This numerical investigation identifies the physics characterizing transient phase change and hydrodynamic interactions of the multi-bubbles during the nucleate boiling.

Luo, Xiao-Yong

2005-11-01

57

Heterogeneous nucleation and growth of the ?(Ti) phase in the Ti-Al system-experiments and model calculations.  

PubMed

The barrier to heterogeneous nucleation of the ?(Ti) phase on TiB(2) and other borides has been evaluated using the plane to plane matching model. The results are compared to the known nucleation of the ?(Ti) phase on the ?(Ti) phase. According to this comparison, the barrier to heterogeneous nucleation of the ?(Ti) phase on TiB(2) can be judged to be small. This is in agreement with inoculation experiments. The addition of a Ti-Al-TiB(2) master composite to a ?(Ti) solidifying TiAl based alloy leads to a significantly refined microstructure. Microsegregations enable us to attribute this refinement to refined equiaxed ?(Ti) dendrites. However, model calculations based on the hemispherical cap model predict that the refinement via heterogeneous ?(Ti) nucleation should be more potent. First calculations indicate that structural imperfections of TiB(2) particles limit the nucleation site diameter. Thereby, the nucleation barrier is increased and the refinement is less pronounced. PMID:21715875

Gosslar, Daniel; Hartig, Christian; Günther, Robert; Hecht, Ulrike; Bormann, Rüdiger

2009-11-18

58

Molecular Dynamics of Simulation of the Nucleation, Growth, Inhibition and Control of Gas Hydrates. Annual Report, April 1991-March 1992.  

National Technical Information Service (NTIS)

This is the first annual report for the Gas Research Institute-funded contract (number 5091-860-2125) entitled 'Molecular Dynamics of Gas Hydrate Nucleation, Growth, Inhibition and Control', covering the period 4/1/91-4/1/92. There were two main objective...

P. Clancy

1992-01-01

59

Nucleation barriers at corners for cubic-to-tetragonal phase transformation  

E-print Network

We are interested in the energetic cost of a martensitic inclusion of volume $V$ in austenite for the cubic-to-tetragonal phase transformation. In contrast with the work of [Kn\\"upfer, Kohn, Otto: Comm. Pure Appl. Math. 66 (2013), no. 6, 867--904], we consider domain with a corner and obtain a better scaling law for the minimal energy ($E_{min} \\sim \\min(V^{2/3},V^{7/9})$). Our predictions are in a good agreement with physical experiments where nucleation of martensite is usually observed near the corners of the specimen.

Peter Bella; Michael Goldman

2013-11-22

60

On the theory of transient nucleation at the intermediate stage of phase transitions  

NASA Astrophysics Data System (ADS)

The evolution of a system of growing aggregates in a macroscopically homogeneous medium with account of both the reduction in metastability and the continuing initiation of new nuclei is studied. The corresponding integro-differential model describing the intermediate stage of phase transitions is solved analytically for arbitrary nucleation kinetics and growth rates of nuclei. An exact solution of the Fokker-Planck equation is found with allowance for the diffusivity along the axis of nucleus radii. In limiting cases of purely kinetic and mixed kinetic-diffusion rates of crystal growth for a special form of diffusivity, the obtained solutions transform to earlier known expressions.

Alexandrov, D. V.

2014-04-01

61

Characterization of the ? phase nucleation in a two-phase metastable ? titanium alloy  

Microsoft Academic Search

Beta titanium alloys are increasingly the best choice for automotive and aerospace applications due to their high performance-to-density\\u000a ratio. Among these alloys, the TIMETAL Ti-LCB is already used in the automotive industry because it presents excellent mechanical\\u000a properties and a lower cost compared with other Ti alloys. The current study deals with the characterization of the nucleation\\u000a and growth of

A. Lenain; N. Clément; P. J. Jacques; M. Véron

2005-01-01

62

Enhancement of heterogeneous nucleation of ?-Sn phases in Sn-rich solders by adding minor alloying elements with hexagonal closed packed structures  

NASA Astrophysics Data System (ADS)

The measured undercooling of pure Sn was about 30 °C due to the difficulty of nucleating a solid ?-Sn phase from a liquid phase. To promote the heterogeneous nucleation of ?-Sn phases, the addition of impurity elements to the solders was suggested. Among the impurity elements, alloying elements with hexagonal closed packed (hcp) structures, such as Co, Zn, Ti, and Mg, were found effective to enhance heterogeneous nucleation of ?-Sn phases in Sn-rich solders. Calculations of the density functional theory indicate that the interfacial energy between ?-Sn and Zn was relatively low. Minor alloying elements with hcp crystals are expected to provide more favorable heterogeneous nucleation sites for ?-Sn phases.

Cho, Moon Gi; Kim, Hyun You; Seo, Sun-Kyoung; Lee, Hyuck Mo

2009-07-01

63

Gas phase atmospheric bromine photochemistry  

Microsoft Academic Search

This paper reviews the current knowledge of gas phase bromine photochemistry and presents a budget study of atmospheric bromine species. The effectiveness of the ozone catalytic loss cycles involving bromine is quantified by considering their chain length and effectiveness. The chain effectiveness is a new variable defined as the chain length multiplied by the rate of the cycle's rate-limiting step.

D. J. Lary

1996-01-01

64

Studies of Nucleation and Growth, Specific Heat and Viscosity of Undercooled Melts of Quasicrystals and Polytetrahedral-Phase-Forming Alloys  

NASA Technical Reports Server (NTRS)

The local atomic structures of undercooled liquid metals are presumed to be icosahedral; this order is incompatible with translational periodicity, constituting a barrier to the nucleation of the crystal phase. The extended atomic structure of the icosahedral quasicrystal (i-phase) is similar to that presumed in the undercooled liquid. Therefore, a comparison of the maximum undercooling in alloys that form the i-phase with those that form crystal phases provides a probe of the liquid structure.

Kelton, K. F.; Gangopadhyay, A. K.; Lee, G. W.; Hyers, R. W.; Rogers, J. R.; Robinson, M. B.; Rathz, T. J.; Krishnan, S.; Curreri, Peter A. (Technical Monitor)

2002-01-01

65

Thin interface analysis of a phase-field model for epitaxial growth with nucleation and Ehrlich-Schwoebel effects  

NASA Astrophysics Data System (ADS)

In this paper, we perform thin interface analysis of a quantitative phase field model for epitaxial growth where nucleation and the Ehrlich-Schwoebel barrier have been considered. Results show that once the nucleation term is introduced into the phase-field model, modification must be carried out to get rid of the extrinsic “kinetic nucleation effect”. While in the ES effect, the asymmetric diffusivity accounts for an irrational step motion that leads the model to deviate from the sharp-interface approximation, hence another modification for the attachment time should be carried. Attributed to these modifications, the phase-field model is more quantitative in describing step flow dynamics in the sharp-interface limit, as well as exhibiting the more convergence of the steady-state velocity with respect to the step width for larger scale simulations. Our analysis and modifications explore the quantitative linking between atom motions and step dynamics.

Dong, X. L.; Xing, H.; Chen, C. L.; Luo, B. C.; Chen, Z.; Zhang, R. L.; Jin, K. X.

2014-11-01

66

Enhancement of heterogeneous nucleation of ?-Sn phases in Sn-rich solders by adding minor alloying elements with hexagonal closed packed structures  

Microsoft Academic Search

The measured undercooling of pure Sn was about 30 °C due to the difficulty of nucleating a solid ?-Sn phase from a liquid phase. To promote the heterogeneous nucleation of ?-Sn phases, the addition of impurity elements to the solders was suggested. Among the impurity elements, alloying elements with hexagonal closed packed (hcp) structures, such as Co, Zn, Ti, and

Moon Gi Cho; Hyun You Kim; Sun-Kyoung Seo; Hyuck Mo Lee

2009-01-01

67

Heterogeneous nucleation of the amorphous phase and dissolution of nanocrystalline grains in bilayer Al-Ge thin films  

SciTech Connect

Solid State Amorphization Reaction (SSAR) was first reported in thin film couples of Au-La by Schwarz et al. Since then, many other systems have been shown to undergo SSAR. Various issues involved in SSAR have been extensively investigated and reviewed. The existence of a large negative heat of mixing, anomalous fast diffusion of one component, the requirement of heterogeneous nucleation sites such as grain boundaries are found to be some of the key features of solid state amorphization. The authors present in this paper evidence of heterogeneous nucleation and growth of the amorphous phase followed by the precipitation of germanium from the amorphous phase in Al-Ge bilayer films.

Raghavan, G.; Divakar, R.; Sundari, T.; Sundararaman, D.; Tyagi, A.K.; Krishan, K. [Indira Gandhi Center for Atomic Research, Kalpakkam (India)] [Indira Gandhi Center for Atomic Research, Kalpakkam (India)

1997-12-18

68

Studies of Nucleation and Growth, Specific Heat and Viscosity of Undercooled Melts of Quasicrystal and Polytetrahedral-Phase Forming Alloys  

NASA Technical Reports Server (NTRS)

From extensive ground based work on the phase diagram and undercooling studies of Ti-Zr-Ni alloys, have clearly identified the composition of three different phases with progressively increasing polytetrahedral order such as, (Ti/Zr), the C14 Laves phase, and the i-phase, that nucleate directly from the undercooled liquid. The reduced undercooling decreases progressively with increasing polytetrahedral order in the solid, supporting Frank s hypothesis. A new facility for direct measurements of the structures and phase transitions in undercooled liquids (BESL) was developed and has provided direct proof of the primary nucleation of a metastable icosahedral phase in some Ti-Zr-Ni alloys. The first measurements of specific heat and viscosity in the undercooled liquid of this alloy system have been completed. Other than the importance of thermo-physical properties for modeling nucleation and growth processes in these materials, these studies have also revealed some interesting new results (such as a maximum of C(sup q, sub p) in the undercooled state). These ground-based results have clearly established the necessary background and the need for conducting benchmark nucleation experiments at the ISS on this alloy system.

Kelton, K. F.; Gangopadhyay, Anup K.; Lee, G. W.; Hyers, Robert W.; Rathz, T. J.; Robinson, Michael B.; Rogers, Jan R.

2003-01-01

69

The Connection Between Local Icosahedral Order in Metallic Liquids and the Nucleation of Ordered Phases  

NASA Technical Reports Server (NTRS)

Over fifty years ago, David Turnbull showed that the temperature of many metallic liquids could be decreased far below their equilibrium melting temperature before crystallization occurred. To explain those surprising results, Charles Frank hypothesized that the local structures of undercooled metallic liquids are different from those of crystal phases, containing a significant degree of icosahedral order that is incompatible with extended periodicity. Such structural differences must create a barrier to the formation crystal phases, explaining the observed undercooling behavior. If true, the nucleation from the liquid of phases with extended icosahedral order should be easier. Icosahedral order is often favored in small clusters, as observed recently in liquid-like clusters of pure Pb on the (111) surface of Si(3), for example. However, it has never been shown that an increasing preference for icosahedral phase formation can be directly linked with the development of icosahedral order in the undercooled liquid. Owing to the combination of very recent advances in levitation techniques and the availability of synchrotron X-ray and high flux neutron facilities.

Kelton, K. F.; Gangopadhyay, A. K.; Lee, G. W.; Hyers, R. W.; Rathz, T. J.; Rogers, J. R.; Robinson, M. B.; Schenk, T.; Simonet, V.; Holland-Moritz, D.; Curreri, Peter A. (Technical Monitor)

2002-01-01

70

The Connection Between Local Icosahedral Order in Metallic Liquids and the Nucleation of Ordered Phases  

NASA Technical Reports Server (NTRS)

Over fifty years ago, David Turnbull showed that the temperature of many metallic liquids could be decreased far below their equilibrium melting temperature before crystallization occurred. To explain those surprising results, Charles Frank hypothesized that the local structures of undercooled metallic liquids are different from those of crystal phases, containing a significant degree of icosahedral order that is incompatible with extended periodicity. Such structural differences must create a barrier to the formation crystal phases, explaining the observed undercooling behavior. If true, the nucleation from the liquid of phases with extended icosahedral order should be easier. Icosahedral order is often favored in small clusters, as observed recently in liquid-like clusters of pure Pb on the (111) surface of Si, for example. However, it has never been shown that an increasing preference for icosahedral phase formation can be directly linked with the development of icosahedral order in the undercooled liquid. Owing to the combination of very recent advances in levitation techniques and the availability of synchrotron x-ray and high flux neutron facilities, this is shown here.

Curreri, Peter A. (Technical Monitor); Kelton, K. F.; Gangopadhyay, A.; Lee, G. W.; Hyers, R. W.; Rathz, R. J.; Rogers, J.; Schenk, T.; Simonet, V.; Holland-Moritz, D.

2003-01-01

71

The Connection Between Local Icosahedral Order in Metallic Liquids and the Nucleation Behavior of Ordered Phases  

NASA Technical Reports Server (NTRS)

Over fifty years ago, David Turnbull showed that the temperature of many metallic liquids could be decreased far below their equilibrium melting temperature before crystallization occurred. To explain those surprising results, Charles Frank hypothesized that the local structures of undercooled metallic liquids are different from those of crystal phases, containing a significant degree of icosahedral order that is incompatible with extended periodicity. Such structural differences must create a barrier to the formation crystal phases, explaining the observed undercooling behavior. If true, the nucleation from the liquid of phases with extended icosahedral order should be easier. Icosahedral order is often favored in small clusters, as observed recently in liquid-like clusters of pure Pb on the (111) surface of Si[3], for example. However, it has never been shown that an increasing preference for icosahedral phase formation can be directly linked with the development of icosahedral order in the undercooled liquid. Owing to the combination of very recent advances in levitation techniques and the availability of synchrotron x-ray and high flux neutron facilities, this is shown here.

Kelton, K. F.; Gangopadhyay, A. K.; Lee, G. W.; Hyers, R. W.; Rathz, T. J.; Rogers, J. R.; Robinson, M. B.; Schenk, T.; Simonet, V.

2003-01-01

72

Distinct Nucleation and Propagation Phases of Northern Cascadia Episodic Tremor and Slip Events  

NASA Astrophysics Data System (ADS)

Northern Cascadia episodic tremor and slip (ETS) events appear to have distinct nucleation and propagation phases. We find that there is a roughly linear increase in tremor amplitude over the first ~5 days of each ETS event. We observe a corresponding linear increase in the areal distribution of tremor. These episodes typically initiate down dip, and after approximately 5 days have organized and migrated to fill the up-dip/down-dip width of the tremorgenic zone. After this time, tremor amplitudes vary wildly, modulated by tidal stresses, as the tremor propagates along strike in one or both directions at roughly 8 km/day, continuing for 4-5 weeks. Inter-ETS tremor swarms can begin similarly to ETS events, but do not reach the maximum area and amplitude of ETS events, and instead die away in less than 5-10 days. Since the increase in tremor amplitude during the nucleation phase is proportional to the increase in tremoring area, the source amplitude per unit area is approximately constant, indicating a constant radiated energy rate per unit area associated with tremor. In order to estimate tremor amplitude we use three-component seismograms from temporary deployments and permanent stations (Array of Arrays, CAFE, PNSN, TA) to estimate the amplitude of tremor bursts at the source location, using a method similar to Maeda and Obara (JGR, 2009). Source amplitude, or radiated energy rate, is proportional to the root-mean square of band limited (1.5-5.5 Hz) ground velocity for each 5-minute window. Station ground velocities and tremor locations, determined by a waveform envelope cross-correlation method (Wech and Creager, GRL, 2008), are inverted to obtain source amplitude and station statics, taking into account geometrical spreading and attenuation. The result is a catalog of source amplitudes for each of 40,000 tremor locations in northern Cascadia from 2006 to 2011.

Ulberg, C.; Creager, K. C.

2013-12-01

73

Molecular dynamics of simulation of the nucleation, growth, inhibition, and control of gas hydrates. Annual report, April 1991March 1992  

Microsoft Academic Search

This is the first annual report for the Gas Research Institute-funded contract (number 5091-860-2125) entitled 'Molecular Dynamics of Gas Hydrate Nucleation, Growth, Inhibition and Control', covering the period 4\\/1\\/91-4\\/1\\/92. There were two main objectives of the research performed in 1991\\/1992: First, it was important to characterize the thermodynamic, structural and kinetic behavior of a computer-simulated hydrate to ensure that the

1992-01-01

74

Polymorphism, crystal nucleation and growth in the phase-field crystal model in 2D and 3D.  

PubMed

We apply a simple dynamical density functional theory, the phase-field crystal (PFC) model of overdamped conservative dynamics, to address polymorphism, crystal nucleation, and crystal growth in the diffusion-controlled limit. We refine the phase diagram for 3D, and determine the line free energy in 2D and the height of the nucleation barrier in 2D and 3D for homogeneous and heterogeneous nucleation by solving the respective Euler-Lagrange (EL) equations. We demonstrate that, in the PFC model, the body-centered cubic (bcc), the face-centered cubic (fcc), and the hexagonal close-packed structures (hcp) compete, while the simple cubic structure is unstable, and that phase preference can be tuned by changing the model parameters: close to the critical point the bcc structure is stable, while far from the critical point the fcc prevails, with an hcp stability domain in between. We note that with increasing distance from the critical point the equilibrium shapes vary from the sphere to specific faceted shapes: rhombic dodecahedron (bcc), truncated octahedron (fcc), and hexagonal prism (hcp). Solving the equation of motion of the PFC model supplied with conserved noise, solidification starts with the nucleation of an amorphous precursor phase, into which the stable crystalline phase nucleates. The growth rate is found to be time dependent and anisotropic; this anisotropy depends on the driving force. We show that due to the diffusion-controlled growth mechanism, which is especially relevant for crystal aggregation in colloidal systems, dendritic growth structures evolve in large-scale isothermal single-component PFC simulations. An oscillatory effective pair potential resembling those for model glass formers has been evaluated from structural data of the amorphous phase obtained by instantaneous quenching. Finally, we present results for eutectic solidification in a binary PFC model. PMID:21386517

Tóth, Gyula I; Tegze, György; Pusztai, Tamás; Tóth, Gergely; Gránásy, László

2010-09-15

75

Experimental studies on nucleation, nanoparticle's formation and polymerization from the vapor phase  

NASA Astrophysics Data System (ADS)

This research is divided into three major parts. In part I, the critical supersaturations required for the homogeneous nucleation of 2,2,2-trifluorothanol (TFE) vapor have been measured over a temperature range (266-296 K) using an upward thermal diffusion cloud chamber (DCC). The measured supersaturations are in agreement with the predictions of both the classical and the scaled theory of nucleation. Moreover, the condensation of supersaturated TFE vapor on laser-vaporized magnesium nanoparticles has been studied under different experimental conditions, such as the supersaturation, the pressure and the electric field. In part II, the laser vaporization controlled condensation (LVCC) technique was used to prepare Au-Ag alloy nanoparticles in the vapor phase using designed targets of compressed Au and Ag micron-sized powder mixtures of selected composition. The results showed that the optical properties of these nanoparticles could be tuned depending on the alloy composition and the laser wavelength. Different intermetallic nanoparticles (FeAl and NiAl) from the vapor phase has also been prepared, using the same approach. In this work, the fraction of the charged particles generated during the laser vaporization process was used to prepare a new class of nanoparticle assemblies in the LVCC chamber under the influence of an electric field. The results showed that the electric field required to induce the formation of these nanoassemblies is material and field dependent. By coupling the LVCC chamber with the differential mobility analyzer, size-selected nanoparticles have been prepared in the vapor phase. The prepared nanoparticles were characterized by different techniques such as scanning electron microscopy (SEM), X-ray diffraction (XRD), transmission electron microscopy (TEM) and UV-visible spectroscopy. In part III, new methods were developed to prepare nanoparticle-polymer composites from the vapor phase. In the first method, the LVCC method was used to prepare a carbonaceous cross-linked resin, with different nanoparticles (Ni, Pt and FeAl) embedded inside. In the second method, free radical-thermally initiated polymerization was used to polymerize a monomer vapor of styrene on the surfaces of activated Ni nanoparticles.

Abdelsayed, Victor Maher

76

Investigating relationships between the seismic "nucleation" phases and breakaway phases of recent Mw 8 earthquakes using global broadband seismic observations  

NASA Astrophysics Data System (ADS)

It is known that the far field P wave velocity observations of large earthquakes frequently start with a small interval of weak motion, which was described as "fore-shock", "pre-shock", or seismic nucleation phase (SNP) by various researchers, e.g, Ellsworth and Beroza (1995). The energetic ground motion immediately following this interesting phase was named as "breakaway" phase. Recent global surveys indicate that for about 50% of Mw>7.5 earthquakes their SNP could be observed teleseismically and the distribution of the earthquakes with SNP appears to be correlated with the tectonic environment and focal mechanisms (Ji et al, 2010; Burkhart and Ji, 2011). Here, a multiple double-couple (MDC) algorithm is developed to quantitatively investigate the relationship between the SNPs and "breakaway" phases of 22 Mw>8 earthquakes since 1990. Our preliminary analysis indicates that the average moment acceleration during the first 4 s of the 2011 Mw 9.1 Tohoku earthquake is only about 2% of that associating with subsequent "breakaway" rupture stage. As the rupture of moderate or large earthquakes often initiate at the vicinity of one of their high slip fault patches, i.e., asperities (Mai et al., 2005), this kind of big discrepancies might shed the light on the intrinsic differences between the asperity and the weak zone in its vicinity, as hypothesized by the asperity theory (e.g., Kanamori, 1981).

Ji, C.

2012-12-01

77

Studies of Nucleation, Growth, Specific Heat, and Viscosity of Undercooled Melts of Quasicrystals and Polytetrahedral-Phase-Forming Alloys  

NASA Technical Reports Server (NTRS)

Undercooling experiments and thermal physical property measurements of metallic alloys on the International Space Station (ISS) are planned. This recently-funded research focuses on fundamental issues of the formation and structure of highly-ordered non-crystallographic phases (quasicrystals) and related crystal phases (crystal approximants), and the connections between the atomic structures of these phases and those of liquids and glasses. It extends studies made previously by us of the composition dependence of crystal nucleation processes in silicate and metallic glasses, to the case of nucleation from the liquid phase. Motivating results from rf-levitation and drop-tube measurements of the undercooling of Ti/Zr-based liquids that form quasicrystals and crystal approximants are discussed. Preliminary measurements by electrostatic levitation (ESL) are presented.

Kelton, K. F.; Croat, T. K.; Gangopadhyay, A.; Holland-Moritz, D.; Hyers, Robert W.; Rathz, Thomas J.; Robinson, Michael B.; Rogers, Jan R.

2001-01-01

78

Ion-induced nucleation in polar one-component fluids  

E-print Network

We present a Ginzburg-Landau theory of ion-induced nucleation in a gas phase of polar one-component fluids, where a liquid droplet grows with an ion at its center. By calculating the density profile around an ion, we show that the solvation free energy is larger in gas than in liquid at the same temperature on the coexistence curve. This difference much reduces the nucleation barrier in a metastable gas.

Hikaru Kitamura; Akira Onuki

2005-08-01

79

AlN heteroepitaxy on sapphire by metalorganic vapour phase epitaxy using low temperature nucleation layers  

NASA Astrophysics Data System (ADS)

Epitaxial films of AlN were grown on a sapphire substrate with a miscut of 0.38°±0.02° towards the m-plane by metalorganic vapour phase epitaxy. A low temperature nucleation layer was used to overcome growth instabilities and to suppress the formation of inversion domains. This was followed by high temperature growth at 1250 °C. This two-step process, gives an acceptable material quality, (0002 FWHM=398±10?? and 10-11 FWHM=940±23??), but resulted in a top surface dominated by large steps, with average heights of 6.0±0.5 nm. Atomic force microscopy analysis of step termination sites shows a staircase of single and double atomic steps, showing large steps are formed by the bunching of single steps, perhaps pinned by threading dislocations. To achieve a smooth top surface, 100 nm of the high temperature AlN is followed by growth at 1110 °C. This three step process largely eliminates the large steps resulting in a layer that has a smooth surface morphology and lower defect density (0002 FWHM=351±9?? and 10-11 FWHM=761±19??).

Li, Haoning; Sadler, Thomas C.; Parbrook, Peter J.

2013-11-01

80

Effect of an alpha-phase nucleating agent on the crystallization kinetics of a propylene/ethylene random copolymer at largely different supercooling  

NASA Astrophysics Data System (ADS)

The effect of addition of 0.1 wt% phosphate-ester based alpha-phase nucleating agent on the crystallization of a random propylene-based copolymer with 3.9 mol% ethylene has been investigated by fast scanning chip calorimetry (FSC). Main purpose of the work was the evaluation of the effect of the nucleating agent on the bimodal temperature dependence of the crystallization rate of propylene-based polymers caused by a change of the nucleation mechanism from heterogeneous to homogeneous nucleation on lowering the temperature to below about 60 °C. Presence of the nucleation agent in the copolymer of the present study accelerates crystallization only in the high-temperature range of predominant heterogeneous nucleation, but does not affect the crystallization rate in the low-temperature range of homogeneous nucleation. The observed decrease of the minimum crystallization half-time due to the addition of the nucleation agent, from 0.2 s in case of the unmodified copolymer to 0.04 s in case of the copolymer containing the nucleating agent, is paralleled by an increase of the critical cooling rate required to inhibit crystallization on continuous cooling to below the glass transition temperature from 102 to 103 K s-1. The study is completed by an analysis of the effect of addition of the nucleation agent on the spherulitic superstructure.

Androsch, René; Monami, Andrea; Kucera, Jaroslav

2014-12-01

81

Rate processes in gas phase  

NASA Technical Reports Server (NTRS)

Reaction-rate theory and experiment are given a critical review from the engineers' point of view. Rates of heavy-particle, collision-induced reaction in gas phase are formulated in terms of the cross sections and activation energies for reaction. The effect of cross section function shape and of excited state contributions to reaction both cause the slope of Arrhenius plots to differ from the true activation energy, except at low temperature. The master equations for chemically reacting gases are introduced, and dissociation and ionization reactions are shown to proceed primarily from excited states about kT from the dissociation or ionization limit. Collision-induced vibration, vibration-rotation, and pure rotation transitions are treated, including three-dimensional effects and conservation of energy, which have usually been ignored. The quantum theory of transitions at potential surface crossing is derived, and results are found to be in fair agreement with experiment in spite of some questionable approximations involved.

Hansen, C. F.

1983-01-01

82

Gas-Phase Spectroscopy of Biomolecular  

E-print Network

Republic, 166 10 Prague 6, Czech Republic; email: pavel.hobza@uochb.cas.cz Annu. Rev. Phys. Chem. 2007. 58 biomolecules into the gas phase intact has largely been solved, making a rich tool chest of gas

de Vries, Mattanjah S.

83

Inclusion phases and the nucleation of acicular ferrite in submerged arc welds in high strength low alloy steels  

Microsoft Academic Search

Series of submerged arc welds of HSLA steel made with three different fluxes and metallic additions of Ti, Mo, and Cr have\\u000a been examined to study the inclusions and their role in the nucleation of acicular ferrite. Inclusion phases and compositions\\u000a have been analyzed by electron diffraction and X-ray microanalysis. These analyses have shown that the inclusions contained\\u000a many different

J. M. Dowling; J. M. Corbett; H. W. Kerr

1986-01-01

84

Transient nucleation in glasses  

NASA Technical Reports Server (NTRS)

Nucleation rates in condensed systems are frequently not at their steady state values. Such time dependent (or transient) nucleation is most clearly observed in devitrification studies of metallic and silicate glasses. The origin of transient nucleation and its role in the formation and stability of desired phases and microstructures are discussed. Numerical models of nucleation in isothermal and nonisothermal situations, based on the coupled differential equations describing cluster evolution within the classical theory, are presented. The importance of transient nucleation in glass formation and crystallization is discussed.

Kelton, K. F.

1991-01-01

85

Numerical model of solid phase transformations governed by nucleation and growth: Microstructure development during isothermal crystallization  

NASA Astrophysics Data System (ADS)

A simple numerical model which calculates the kinetics of crystallization involving randomly distributed nucleation and isotropic growth is presented. The model can be applied to different thermal histories and no restrictions are imposed on the time and the temperature dependences of the nucleation and growth rates. We also develop an algorithm which evaluates the corresponding emerging grain-size distribution. The algorithm is easy to implement and particularly flexible, making it possible to simulate several experimental conditions. Its simplicity and minimal computer requirements allow high accuracy for two- and three-dimensional growth simulations. The algorithm is applied to explore the grain morphology development during isothermal treatments for several nucleation regimes. In particular, thermal nucleation, preexisting nuclei, and the combination of both nucleation mechanisms are analyzed. For the first two cases, the universal grain-size distribution is obtained. The high accuracy of the model is stated from its comparison to analytical predictions. Finally, the validity of the Kolmogorov-Johnson-Mehl-Avrami model [J. Chem. Phys. 7, 1103 (1939); 8, 212 (1940); 9, 177 (1941); Trans. Am. Inst. Min., Metall. Pet. Eng. 135, 416 (1939); Izv. Akad. Nauk SSSR, Ser. Fiz. 1, 355 (1937)] is verified for all the cases studied.

Farjas, Jordi; Roura, Pere

2007-05-01

86

The homogeneous nucleation of 1-pentanol in a laminar flow diffusion chamber: The effect of pressure and kind of carrier gas  

NASA Astrophysics Data System (ADS)

The influence of total pressure and kind of carrier gas on homogeneous nucleation rates of 1-pentanol was investigated using experimental method of laminar flow diffusion chamber in this study. Two different carrier gases (helium and argon) were used in the total pressure range from 50 to 400 kPa. Nucleation temperatures ranged from 265 to 290 K for 1-pentanol-helium and from 265 to 285 K for 1-pentanol-argon. Nucleation rates varied between 101 and 106 cm-3 s-1 for 1-pentanol-helium and between 102 and 105 cm-3 s-1 for 1-pentanol-argon. Both positive and slight negative pressure effects were observed depending on temperature and carrier gas. The trend of pressure effect was found similar for both carrier gases. Error analysis on thermodynamic properties was conducted, and the lowering of surface tension due to adsorption of argon on nucleated droplets was estimated. A quantitative overview of pressure effect is provided.

Brus, D.; Hyvärinen, A.-P.; Wedekind, J.; Viisanen, Y.; Kulmala, M.; Ždímal, V.; Smolík, J.; Lihavainen, H.

2008-04-01

87

Phase-field Modeling of Gas Bubbles and Thermal Conductivity Evolution in Nuclear Fuels  

SciTech Connect

The major factors that influence the thermal conductivity of the ceramics and metals are temperature, stoichiometry, microstructure, porosity, and point defects. Nuclear fuels and structure materials are subject to a severe radiation environment and their properties, including thermal conductivity change significantly with time and irradiation level. In particular, the accumulation of fission products and the formation of He bubbles can decrease the heat transfer, leading to overheating of the fuel element. In this work, we use the phase-field method to study the effect of microstructural changes on thermal conductivity. We developed a phase-field model to simulate the He bubble formation and growth in a single/polycrystalline material with defects. The model takes into account the generation of gas atoms and defects, gas atom diffusivity inhomogeneity, gas atom segregation, and gas bubble nucleation. With the model, we simulated the gas bubble and temperature evolution, and calculated the effect of gas bubble volume fraction on effective thermal conductivity.

Hu, Shenyang Y.; Henager, Charles H.; Heinisch, Howard L.; Stan, Marius; Baskes, Michael I.; Valone, Steven

2009-07-15

88

Grain structures in gas tungsten-arc welds of austenitic stainless steels with ferrite primary phase  

Microsoft Academic Search

The grain structures were investigated in full penetration gas tungsten-arc (GTA) welds in sheets of 304 and 321 austenitic\\u000a stainless steels for a range of welding conditions. In type 321 steel welds, fine equiaxed ferrite dendrites were observed\\u000a in the ferrite phase. The equiaxed structure was ascribed to heterogeneous nucleation of ferrite on Ti-rich cuboidal inclusions\\u000a present in this steel,

J. C. Villafuerte; H. W. Kerr

1990-01-01

89

Microstructual path analysis of polycrystalline solidification by using multi-phase-field method incorporating a nucleation model  

NASA Astrophysics Data System (ADS)

Using the multi-phase-field (MPF) method incorporating a continuous nucleation model, we have revisited polycrystalline solidification described by the KJMA kinetics. Besides the Avrami exponents, the microstructural path functions to quantify the morphological characteristics were calculated within the framework of the MPF method. Our simulation can easily take account of the effects that are difficult to deduce from the conventional KJMA theory such as grain impingement and spatial distribution of crystallite seeds. As a result, quantitative differences among various types of transformation kinetics can be identified.

Nishida, Yasutaka; Aiga, Fumihiko; Itoh, Satoshi

2014-11-01

90

Gas-Phase Infrared; JCAMP Format  

National Institute of Standards and Technology Data Gateway

SRD 35 NIST/EPA Gas-Phase Infrared; JCAMP Format (PC database for purchase)   This data collection contains 5,228 infrared spectra in the JCAMP-DX (Joint Committee for Atomic and Molecular Physical Data "Data Exchange") format.

91

Quantification of gypsum crystal nucleation, growth, and breakage rates in a wet flue gas desulfurization pilot plant  

SciTech Connect

The aim of this work is to study the influence of nucleation, growth and breakage on the particle size distribution (PSD) of gypsum crystals produced by the wet flue gas desulfurization (FGD) process. The steady state PSD, obtained in a falling film wet FGD pilot plant during desulfurization of a 1000 ppm(V) SO{sub 2} gas stream, displayed a strong nonlinear behaviour (in a ln(n(l)) vs. I plot) at the lower end of the particle size range, compared to the well-known linear mixed suspension mixed product removal model. A transient population balance breakage model, fitted to experimental data, was able to model an increase in the fraction of small particles, but not to the extent observed experimentally. A three-parameter, size-dependent growth model, previously used for sodium sulphate decahydrate and potash alum, was able to describe the experimental data, indicating either size-dependent integration kinetics or growth rate dispersion.

Hansen, B.B.; Kiil, S.; Johnsson, J.E. [Technical University of Denmark, Lyngby (Denmark). Dept. of Chemical & Biochemical Engineering

2009-10-15

92

Cryogenic two-phase flow during chilldown: Flow transition and nucleate boiling heat transfer  

NASA Astrophysics Data System (ADS)

The recent interest in space exploration has placed a renewed focus on rocket propulsion technology. Cryogenic propellants are the preferred fuel for rocket propulsion since they are more energetic and environmentally friendly compared with other storable fuels. Voracious evaporation occurs while transferring these fluids through a pipeline that is initially in thermal equilibrium with the environment. This phenomenon is referred to as line chilldown. Large temperature differences, rapid transients, pressure fluctuations and the transition from the film boiling to the nucleate boiling regime characterize the chilldown process. Although the existence of the chilldown phenomenon has been known for decades, the process is not well understood. Attempts have been made to model the chilldown process; however the results have been fair at best. A major shortcoming of these models is the use of correlations that were developed for steady, non-cryogenic flows. The development of reliable correlations for cryogenic chilldown has been hindered by the lack of experimental data. An experimental facility was constructed that allows the flow structure, the temperature history and the pressure history to be recorded during the line chilldown process. The temperature history is then utilized in conjunction with an inverse heat conduction procedure that was developed, which allows the unsteady heat transfer coefficient on the interior of the pipe wall to be extracted. This database is used to evaluate present predictive models and correlations for flow regime transition and nucleate boiling heat transfer. It is found that by calibrating the transition between the stratified-wavy and the intermittent/annular regimes of the Taitel and Dukler flow regime map, satisfactory predictions are obtained. It is also found that by utilizing a simple model that includes the effect of flow structure and incorporating the enhancement provided by the local heat flux, significant improvement in the predictive capabilities of the Muller-Steinhagen and Jamialahmadi correlation for nucleate flow boiling is achieved.

Jackson, Jelliffe Kevin

93

Project ARGO: Gas phase formation in simulated microgravity  

NASA Technical Reports Server (NTRS)

The ARGO study investigated the reduced incidence of joint pain decompression sickness (DCS) encountered in microgravity as compared with an expected incidence of joint pain DCS experienced by test subjects in Earth-based laboratories (unit gravity) with similar protocols. Individuals who are decompressed from saturated conditions usually acquire joint pain DCS in the lower extremities. Our hypothesis is that the incidence of joint pain DCS can be limited by a significant reduction in the tissue gas micronuclei formed by stress-assisted nucleation. Reductions in dynamic and kinetic stresses in vivo are linked to hypokinetic and adynamic conditions of individuals in zero g. We employed the Doppler ultrasound bubble detection technique in simulated microgravity studies to determine quantitatively the degree of gas phase formation in the upper and lower extremities of test subjects during decompression. We found no evidence of right-to-left shunting through pulmonary vasculature. The volume of gas bubble following decompression was examined and compared with the number following saline contrast injection. From this, we predict a reduced incidence of DCS on orbit, although the incidence of predicted mild DCS still remains larger than that encountered on orbit.

Powell, Michael R.; Waligora, James M.; Norfleet, William T.; Kumar, K. Vasantha

1993-01-01

94

Studies on pressure response of gas bubbles contributions of condensed droplets in bubbles generated by a uniform nucleation  

NASA Technical Reports Server (NTRS)

The response of a tiny gas bubble under reduced pressure is investigated in its relation to cavitation. Equations of motion are formulated for gas mixtures inside the bubble and numerical calculations performed for several examples. The conclusions are as follows: (1) at the onset of bubble growth, the gas mixture inside it adiabatically expands and the temperature decreases. Condensed droplets appear inside the gas mixture due to a uniform nucleation and the temperature recovers, thus the motion of the bubble is apparently isothermal; (2) the evaporation and condensation coefficient largely affects bubble motions (maximum radius, period and rate of attenuation of the bubble oscillation) including the uniform contraction; (3) the oscillation period of the bubble is longer as the equilibrium bubble radius is larger when the surrounding pressure decreases stepwise. In this circumstance the temperature inside the bubble is kept constant due to condensation evaporation phenomena and is nearly isothermal; and (4) when the surrounding pressure decreases in a stepwise fashion, the critical pressure bubble radius relation becomes closer to that for the isothermal process if the bubble radius is larger than 8 microns.

Matsumoto, Y.

1988-01-01

95

Tetragonal Lysozyme Nucleation and Crystal Growth: The Role of the Solution Phase  

NASA Technical Reports Server (NTRS)

Lysozyme, and most particularly the tetragonal form of the protein, has become the default standard protein for use in macromolecule crystal nucleation and growth studies. There is a substantial body of experimental evidence, from this and other laboratories, that strongly suggests this proteins crystal nucleation and growth is by addition of associated species that are preformed by standard reversible concentration-driven self association processes in the bulk solution. The evidence includes high resolution AFM studies of the surface packing and of growth unit size at incorporation, fluorescence resonance energy transfer measurements of intermolecular distances in dilute solution, dialysis kinetics, and modeling of the growth rate data. We have developed a selfassociation model for the proteins crystal nucleation and growth. The model accounts for the obtained crystal symmetry, explains the observed surface structures, and shows the importance of the symmetry obtained by self-association in solution to the process as a whole. Further, it indicates that nucleation and crystal growth are not distinct mechanistically, but identical, with the primary difference being the probability that the particle will continue to grow or dissolve. This model also offers a possible mechanism for fluid flow effects on the growth process and how microgravity may affect it. While a single lysozyme molecule is relatively small (M.W. = 14,400), a structured octamer in the 4(sub 3) helix configuration (the proposed average sized growth unit) would have a M.W. = 115,000 and dimensions of 5.6 x 5.6 x 7.6 nm. Direct AFM measurements of growth unit incorporation indicate that units as wide as 11.2 nm and as long as 11.4 nm commonly attach to the crystal. These measurements were made at approximately saturation conditions, and they reflect the sizes of species that both added or desorbed from the crystal surface. The larger and less isotropic the associated species the more likely that it will be oriented to some degree in a flowing boundary layer, even at the low flow velocities measured about macromolecule crystals. Flow-driven effects resulting in misorientation upon addition to and incorporation into the crystal need only be a small fraction of a percentage to significantly affect the resulting crystal. One Earth, concentration gradient driven flow will maintain a high interfacial concentration, i.e., a high level (essentially that of the bulk solution) of solute association at the interface and higher growth rate. Higher growth rates mean an increased probability that misaligned growth units are trapped by subsequent growth layers before they can be desorbed and try again, or that the desorbing species will be smaller than the adsorbing species. In microgravity the extended diffusive boundary layer will lower the interfacial concentration. This results in a net dissociation of aggregated species that diffuse in from the bulk solution, i.e., smaller associated species, which are more likely able to make multiple attempts to correctly bind, yielding higher quality crystals.

Pusey, Marc L.; Forsythe, Elizabeth; Sumida, John; Maxwell, Daniel; Gorti, Sridhar

2002-01-01

96

Tetragonal Lysozyme Nucleation and Crystal Growth: The Role of the Solution Phase  

NASA Astrophysics Data System (ADS)

Lysozyme, and most particularly the tetragonal form of the protein, has become the default standard protein for use in macromolecule crystal nucleation and growth studies. There is a substantial body of experimental evidence, from this and other laboratories, that strongly suggests this proteins crystal nucleation and growth is by addition of associated species that are preformed by standard reversible concentration-driven self association processes in the bulk solution. The evidence includes high resolution AFM studies of the surface packing and of growth unit size at incorporation, fluorescence resonance energy transfer measurements of intermolecular distances in dilute solution, dialysis kinetics, and modeling of the growth rate data. We have developed a selfassociation model for the proteins crystal nucleation and growth. The model accounts for the obtained crystal symmetry, explains the observed surface structures, and shows the importance of the symmetry obtained by self-association in solution to the process as a whole. Further, it indicates that nucleation and crystal growth are not distinct mechanistically, but identical, with the primary difference being the probability that the particle will continue to grow or dissolve. This model also offers a possible mechanism for fluid flow effects on the growth process and how microgravity may affect it. While a single lysozyme molecule is relatively small (M.W. = 14,400), a structured octamer in the 43 helix configuration (the proposed average sized growth unit) would have a M.W. = 115,000 and dimensions of 5.6 x 5.6 x 7.6 nm. Direct AFM measurements of growth unit incorporation indicate that units as wide as 11.2 nm and as long as 11.4 nm commonly attach to the crystal. These measurements were made at approximately saturation conditions, and they reflect the sizes of species that both added or desorbed from the crystal surface. The larger and less isotropic the associated species the more likely that it will be oriented to some degree in a flowing boundary layer, even at the low flow velocities measured about macromolecule crystals. Flow-driven effects resulting in misorientation upon addition to and incorporation into the crystal need only be a small fraction of a percentage to significantly affect the resulting crystal. One Earth, concentration gradient driven flow will maintain a high interfacial concentration, i.e., a high level (essentially that of the bulk solution) of solute association at the interface and higher growth rate. Higher growth rates mean an increased probability that misaligned growth units are trapped by subsequent growth layers before they can be desorbed and try again, or that the desorbing species will be smaller than the adsorbing species. In microgravity the extended diffusive boundary layer will lower the interfacial concentration. This results in a net dissociation of aggregated species that diffuse in from the bulk solution, i.e., smaller associated species, which are more likely able to make multiple attempts to correctly bind, yielding higher quality crystals.

Pusey, Marc L.; Forsythe, Elizabeth; Sumida, John; Maxwell, Daniel; Gorti, Sridhar

2002-11-01

97

Real Gas/Blunt Cone. Phase 2  

NASA Technical Reports Server (NTRS)

In this chapter recent activity in real-gas database definition and code validation will be summarized. In the Phase I report of the Working Group (WG) 181, aerothermodynamic problems were classified, for purpose of discussion, into seven types: aerodynamic parameters, viscous/shock interaction, boundary-layer transition, forebody-heating/heat-transfer, radiation and ablation, lee and base-region flow, and low-density flow. Several of these problem types were the subject of various chapters of the Phase 1 report describing real-gas effects and ground test facility issues. In this chapter some background and objectives outlined in the real-Gas effects Chapter V of the Phase 1 report will be reviewed. The results of the blunt cone test campaign developed under the auspices of the WG18 activity to study real-gas phenomena will be summarized, including the experimental and computational programs, issues and questions, and recommendations. Further, recent progress in other real-gas areas beyond the blunt cone test campaign will be discussed. Finally, a summary in which the present status of our understanding of real-gas issues will be presented.

Deiwert, George S.; Eitelberg, Georg

1998-01-01

98

Further Investigation into the Seismic Nucleation Phase of Large Earthquakes with a Focus on Strike-Slip Events  

NASA Astrophysics Data System (ADS)

The dynamic motion of an earthquake begins abruptly, but is often initiated by a small interval of weak motion called the seismic nucleation phase (SNP), first named by Ellsworth and Beroza (1995). In their study, Ellsworth and Beroza (1995, 1996) concluded that the SNP was detectable in near-source records of all of the 41 M 1 to M 8 earthquakes they investigated, with the SNP accounting for ~0.5% of the total moment and lasting ~1/6 of the total duration. Concentrating on large earthquakes, Ji et al (2010) investigated the SNP of 19 M 8.0 earthquakes since 1994 using a new approach applied to teleseismic broadband data. They found that ~50% of the earthquakes had a detectable SNP. Burkhart and Ji (2011) found that, in 68 M 7.5 to M 8.0 since 1994, the SNP is clearly detectable in 31 events, with 27 events showing no nucleation phase and 10 having too much noise or not enough stations to tell. After making modifications to the stacking code allowing for more specific station choice, these earthquakes have all been re-examined, and a consistent finding is that strike-slip earthquakes are more likely to exhibit a clear SNP than normal or thrust earthquakes. Continuing to investigate these events, this study finds further conclusive evidence that large shallow, continental, and strike-slip earthquakes show a clear SNP. We find that 11 of the 15 strike-slip earthquakes investigated show a clear SNP, with three having none (including the 2002 Mw 7.8 Denali Fault earthquake, which initiated as a thrust subevent), and one with not enough stations to perform stacking.

Burkhart, E.; Ji, C.

2012-12-01

99

Continuous-Flow Gas-Phase Bioreactors  

NASA Technical Reports Server (NTRS)

Continuous-flow gas-phase bioreactors proposed for biochemical, food-processing, and related industries. Reactor contains one or more selected enzymes dehydrated or otherwise immobilized on solid carrier. Selected reactant gases fed into reactor, wherein chemical reactions catalyzed by enzyme(s) yield product biochemicals. Concept based on discovery that enzymes not necessarily placed in traditional aqueous environments to function as biocatalysts.

Wise, Donald L.; Trantolo, Debra J.

1994-01-01

100

EPA GAS PHASE CHEMISTRY CHAMBER STUDIES  

EPA Science Inventory

Gas-phase smog chamber experiments are being performed at EPA in order to evaluate a number of current chemical mechanisms for inclusion in EPA regulatory and research models. The smog chambers are 9000 L in volume and constructed of 2-mil teflon film. One of the chambers is co...

101

Molecular dynamics of simulation of the nucleation, growth, inhibition, and control of gas hydrates. Annual report, April 1991-March 1992  

SciTech Connect

This is the first annual report for the Gas Research Institute-funded contract (number 5091-860-2125) entitled 'Molecular Dynamics of Gas Hydrate Nucleation, Growth, Inhibition and Control', covering the period 4/1/91-4/1/92. There were two main objectives of the research performed in 1991/1992: First, it was important to characterize the thermodynamic, structural and kinetic behavior of a computer-simulated hydrate to ensure that the predictions of the simulations were likely to be an accurate representation of the behavior of the real physical system. Second, the authors performed an investigation of the kinetics of crystal growth and dissolution in order to develop appropriate methods for extracting kinetic data from the raw simulation data. The research has led to the production of a considerable body of previously unknown information about the behavior of hydrate-forming mixtures and has provided atomic-scale mechanistic explanations for the origin of a number of experimentally-verified observations about hydrate formation, for example, in explaining why hydrate forming occurs more readily at a liquid/vapor interface than under any other conditions.

Clancy, P.

1992-05-01

102

Infrared spectroscopy of homogeneously nucleated hydrazine aerosols - Disordered and crystalline phases. [in planetary atmospheres  

NASA Technical Reports Server (NTRS)

It is shown that aerosols generated at low temperatures and high condensation rate spontaneously form in a highly crystalline state. The resonant absorption bands in the IR spectra of these highly crystalline particles are much sharper than any reported previously in the bulk, and reveal details in the N-H vibrational bands that have not been previously observed. A disordered phase is also observed at somewhat higher temperatures. These results are consistent with this being a supercooled liquid. The fact that the spectra associated with these two aerosol phases are quite different is important to any future attempts at detecting hydrazine aerosols in planetary atmospheres by remote sensing techniques.

Dunder, T.; Clapp, M. L.; Miller, R. E.

1993-01-01

103

Differences in nucleator adsorption may explain distinct inhibition activities of two gas hydrate kinetic inhibitors  

Microsoft Academic Search

Pipeline blockage by gas hydrate is a serious problem in petroleum industry. Recently, low-dosage inhibitors have been developed. In particular, poly(N-vinylcaprolactam) (PVCap) is a stronger inhibitor than poly(N-vinylpyrrolidone) (PVP). In this study, PVCap was also found to have stronger inhibition activity compared to PVP, but it was less effective during reformation of hydrate. To understand the mechanism, the adsorption of

Huang Zeng; Hailong Lu; Emily Huva; Virginia K. Walker; John A. Ripmeester

2008-01-01

104

On the nucleation and propagation of phase transformation fronts in a NiTi alloy  

Microsoft Academic Search

In this paper we present an experimental methodology for simultaneous full field monitoring of the deformation and thermal changes in NiTi during mechanically unstable regimes associated with the pseudoelastic material response. The deformation history is established by photographically recording surface changes of a brittle coating as austenite-martensite phase transition fronts traverse the specimen. Temperature changes are monitored by infrared thermal

J. A. Shaw; S. Kyriakides

1997-01-01

105

Isothermal nucleation and growth kinetics of Pd/Ag alloy phase via in-situ time-resolved high-temperature x-ray diffraction (HTXRD) analysis  

SciTech Connect

Among several different approaches to form Pd/Ag alloys for hydrogen separation applications, ex-situ studies carried by conventional X-ray point scanning detectors might fail to reveal the key aspects of the phase transformation between Pd and Ag metals. In this respect, in-situ time-resolved high temperature X-ray diffraction (HTXRD) was employed to study the Pd/Ag alloy phase nucleation and growth kinetics. By the use of linear position sensitive detectors, advanced optics and profile fitting with the use of JADE-6.5 software, isothermal phase evolution of the Pd/Ag alloy at 500 C, 550 C and 600 C under hydrogen atmosphere were quantified to elucidate the mechanistic details of the Pd/Ag alloy phase nucleation and growth pattern. Analysis of the HTXRD data by the Avrami model indicated that the nucleation of the Pd/Ag alloy phase was instantaneous where the growth mechanism was through diffusion-controlled one-dimensional thickening of the Pd/Ag alloy layer. The value of the Avrami exponent, n, was found to increase with temperature with the values of 0.34, 0.39 and 0.67 at 500oC, 550oC and 600oC, respectively. In addition, parabolic rate law analysis suggested that the nucleation of the Pd/Ag alloy phase was through a heterogeneous nucleation mode, in which the nucleation sites were defined as the non-equilibrium defects. The cross-sectional SEI micrographs indicated that the Pd/Ag alloy phase growth was strongly dependent upon the deposition morphology of the as-synthesized Pd and Ag layers formed by the electroless plating. Based on the Avrami model and the parabolic rate law, the estimated activation energies for the phase transformation were 236.5 and 185.6 kJ/mol and in excellent agreement with the literature values (183-239.5 kJ/mol).

Ayturk, Mahmut Engin [Worcester Polytechnic Institute; Payzant, E Andrew [ORNL; Speakman, Scott A [ORNL; Ma, Yi Hua [Worcester Polytechnic Institute

2008-01-01

106

Gas-phase optically pumped infrared lasers  

Microsoft Academic Search

This experimental research program is designed to assess the possibility of using gas-phase optically pumped lasers (OPL) as efficient, frequency-agile mid-infrared sources. The eventual goal will be to incorporate efficient diode lasers into the pumping step, either by direct frequency stabilized diode pumping or by pumping with diode-pumped solid state lasers. In this paper, we discuss experiments on a optically

Harold C. Miller; Dan T. Radzykewycz; Gordon D. Hager; William J. Kessler; Steven J. Davis

1993-01-01

107

Gas-Phase Protonation Thermochemistry of Adenosine  

Microsoft Academic Search

The goal of this work was to obtain a detailed insight on the gas-phase protonation energetic of adenosine using both mass spectrometric experiments and quantum chemical calculations. The experimental approach used the extended kinetic method with nanoelectrospray ionization and collision-induced dissociation tandem mass spectrometry. This method provides experimental values for proton affinity, PA(adenosine) ) 979 ( 1 kJ ·mol-1, and

David Touboul; Guy Bouchoux; Renato Zenobi

2008-01-01

108

Nucleation mechanism of the eutectic phases in aluminum-silicon hypoeutectic alloys  

SciTech Connect

A theory is presented to explain the mechanism of formation of the eutectic phases in Al-Si hypoeutectic alloys. Results include optical, scanning and transmission electron microscopy, as well as selected area electron diffraction analysis and elemental X-ray mapping performed on Al-Si hypoeutectic alloy samples. The alloy samples had precisely controlled chemistry and were solidified at various cooling rates. The data presented support the proposed theory with microstructural and crystallographic evidence.

Shankar, Sumanth; Riddle, Yancy W.; Makhlouf, Makhlouf M

2004-09-06

109

Polymorphic phase transition among the titania crystal structures using a solution-based approach: from precursor chemistry to nucleation process  

NASA Astrophysics Data System (ADS)

Nanocrystalline titania are a robust candidate for various functional applications owing to its non-toxicity, cheap availability, ease of preparation and exceptional photochemical as well as thermal stability. The uniqueness in each lattice structure of titania leads to multifaceted physico-chemical and opto-electronic properties, which yield different functionalities and thus influence their performances in various green energy applications. The high temperature treatment for crystallizing titania triggers inevitable particle growth and the destruction of delicate nanostructural features. Thus, the preparation of crystalline titania with tunable phase/particle size/morphology at low to moderate temperatures using a solution-based approach has paved the way for further exciting areas of research. In this focused review, titania synthesis from hydrothermal/solvothermal method, conventional sol-gel method and sol-gel-assisted method via ultrasonication, photoillumination and ILs, thermolysis and microemulsion routes are discussed. These wet chemical methods have broader visibility, since multiple reaction parameters, such as precursor chemistry, surfactants, chelating agents, solvents, mineralizer, pH of the solution, aging time, reaction temperature/time, inorganic electrolytes, can be easily manipulated to tune the final physical structure. This review sheds light on the stabilization/phase transformation pathways of titania polymorphs like anatase, rutile, brookite and TiO2(B) under a variety of reaction conditions. The driving force for crystallization arising from complex species in solution coupled with pH of the solution and ion species facilitating the orientation of octahedral resulting in a crystalline phase are reviewed in detail. In addition to titanium halide/alkoxide, the nucleation of titania from other precursors like peroxo and layered titanates are also discussed. The non-aqueous route and ball milling-induced titania transformation is briefly outlined; moreover, the lacunae in understanding the concepts and future prospects in this exciting field are suggested.

Kumar, S. Girish; Rao, K. S. R. Koteswara

2014-09-01

110

Polymorphic phase transition among the titania crystal structures using a solution-based approach: from precursor chemistry to nucleation process.  

PubMed

Nanocrystalline titania are a robust candidate for various functional applications owing to its non-toxicity, cheap availability, ease of preparation and exceptional photochemical as well as thermal stability. The uniqueness in each lattice structure of titania leads to multifaceted physico-chemical and opto-electronic properties, which yield different functionalities and thus influence their performances in various green energy applications. The high temperature treatment for crystallizing titania triggers inevitable particle growth and the destruction of delicate nanostructural features. Thus, the preparation of crystalline titania with tunable phase/particle size/morphology at low to moderate temperatures using a solution-based approach has paved the way for further exciting areas of research. In this focused review, titania synthesis from hydrothermal/solvothermal method, conventional sol-gel method and sol-gel-assisted method via ultrasonication, photoillumination and ILs, thermolysis and microemulsion routes are discussed. These wet chemical methods have broader visibility, since multiple reaction parameters, such as precursor chemistry, surfactants, chelating agents, solvents, mineralizer, pH of the solution, aging time, reaction temperature/time, inorganic electrolytes, can be easily manipulated to tune the final physical structure. This review sheds light on the stabilization/phase transformation pathways of titania polymorphs like anatase, rutile, brookite and TiO2(B) under a variety of reaction conditions. The driving force for crystallization arising from complex species in solution coupled with pH of the solution and ion species facilitating the orientation of octahedral resulting in a crystalline phase are reviewed in detail. In addition to titanium halide/alkoxide, the nucleation of titania from other precursors like peroxo and layered titanates are also discussed. The non-aqueous route and ball milling-induced titania transformation is briefly outlined; moreover, the lacunae in understanding the concepts and future prospects in this exciting field are suggested. PMID:24969423

Kumar, S Girish; Rao, K S R Koteswara

2014-09-25

111

Homogeneous nucleation kinetics  

NASA Technical Reports Server (NTRS)

Homogeneous nucleation kinetics are rederived in a manner fundamentally similar to the approach of classical nucleation theory with the following modifications and improvements. First, the cluster is a parent phase cluster and does not require energization to the parent state. Second, the thermodynamic potential used to describe phase stability is a continuous function along the pathway of phase decomposition. Third, the kinetics of clustering corresponds directly to the diffusional flux of monomers through the cluster distribution and are formally similar to classical theory with the resulting kinetic equation modified by two terms in the preexponential factor. These terms correct for the influence of a supersaturation dependent clustering within the parent phase and for the influence of an asymmetrical cluster concentration as a function of cluster size at the critical cluster size. Fourth, the supersaturation dependence of the nucleation rate is of the same form as that given by classical nucleation theory. This supersaturation dependence must however be interpreted in terms of a size dependent surface tension. Finally, there are two scaling laws which describe supersaturation to either constant nucleation rate or to the thermodynamically determined physical spinodal.

Rasmussen, D. H.; Appleby, M. R.; Leedom, G. L.; Babu, S. V.; Naumann, R. J.

1983-01-01

112

Homogeneous nucleation kinetics  

NASA Astrophysics Data System (ADS)

Homogeneous nucleation kinetics are rederived in a manner fundamentally similar to the approach of classical nucleation theory with the following modifications and improvements. First, the cluster is a parent phase cluster and does not require energization to the parent state. Second, the thermodynamic potential used to describe phase stability is a continuous function along the pathway of phase decomposition. Third, the kinetics of clustering corresponds directly to the diffusional flux of monomers through the cluster distribution and are formally similar to classical theory with the resulting kinetic equation modified by two terms in the preexponential factor. These terms correct for the influence of a supersaturation dependent clustering within the parent phase and for the influence of an asymmetrical cluster concentration as a function of cluster size at the critical cluster size. Fourth, the supersaturation dependence of the nucleation rate is of the same form as that given by classical nucleation theory. This supersaturation dependence must however be interpreted in terms of a size dependent surface tension. Finally, there are two scaling laws which describe supersaturation to either constant nucleation rate or to the thermodynamically determined physical spinodal.

Rasmussen, D. H.; Appleby, M. R.; Leedom, G. L.; Babu, S. V.; Naumann, R. J.

1983-11-01

113

Stabilized enzymes in continuous gas phase reactions  

SciTech Connect

We are assessing the utility of enzymes to catalyze reactions in a continuous gas phase reactor. First, alcohol dehydrogenase has been used to oxidize an unsaturated alcohol, 3-methyl-2-buten-1-ol (UOL), to the corresponding unsaturated aldehyde, 3-methyl-2-butenal (UAL). Cofactor NAD{sup +} was regenerated by concomitant acetone reduction to isopropyl alcohol. Second, organophosphorus hydrolase (OPH) has been used to hydrolyze pesticide vapors. In order to control enzyme hydration level, enzyme water adsorption isotherms at different temperature have been studied. Huttig`s isotherm model has been found suitable to describe adsorption behavior. The influence of enzyme hydration level, enzyme loading on glass beads, reaction temperature and flow rate on enzymatic reaction rate and biocatalyst stability were investigated. Reaction kinetics were studied and a kinetic model was proposed. We will also report our attempts to further stabilize enzymes for use in gas reactions by incorporating them into polymer matrices.

Yang, Fangxiao; LeJeune, K.; Yang, Zhen [Univ. of Pittsburgh, PA (United States)] [and others

1995-12-01

114

Gas phase thermochemistry of organogermanium compounds  

SciTech Connect

A variety of silyl- and alkyl-germylene precursors have been synthesized and subsequently pyrolyzed in the gas phase. Arrhenius parameters were obtained employing a pulsed-stirred flow reactor for these unimolecular decompositions. These precursors are divided into two major categories by mechanism of germylene extrusion: {alpha}-elimination precursors and germylacetylenes. The extrusion of germylenes from germylacetylene precursors is of primary interest. A mechanism is proposed employing a germacyclopropene intermediate. Evidence supporting this mechanism is presented. In the process of exploring germylacetylenes as germylene precursors, an apparent dyatropic rearrangement between germanium and silicon was observed. This rearrangement was subsequently explored.

Engel, J.P.

1993-12-07

115

Vaccum Gas Tungsten Arc Welding, phase 1  

NASA Astrophysics Data System (ADS)

This two year program will investigate Vacuum Gas Tungsten Arc Welding (VGTAW) as a method to modify or improve the weldability of normally difficult-to-weld materials. VGTAW appears to offer a significant improvement in weldability because of the clean environment and lower heat input needed. The overall objective of the program is to develop the VGTAW technology and implement it into a manufacturing environment that will result in lower cost, better quality and higher reliability aerospace components for the space shuttle and other NASA space systems. Phase 1 of this program was aimed at demonstrating the process's ability to weld normally difficult-to-weld materials. Phase 2 will focus on further evaluation, a hardware demonstration and a plan to implement VGTAW technology into a manufacturing environment. During Phase 1, the following tasks were performed: (1) Task 11000 Facility Modification - an existing vacuum chamber was modified and adapted to a GTAW power supply; (2) Task 12000 Materials Selection - four difficult-to-weld materials typically used in the construction of aerospace hardware were chosen for study; (3) Task 13000 VGTAW Experiments - welding experiments were conducted under vacuum using the hollow tungsten electrode and evaluation. As a result of this effort, two materials, NARloy Z and Incoloy 903, were downselected for further characterization in Phase 2; and (4) Task 13100 Aluminum-Lithium Weld Studies - this task was added to the original work statement to investigate the effects of vacuum welding and weld pool vibration on aluminum-lithium alloys.

Weeks, J. L.; Krotz, P. D.; Todd, D. T.; Liaw, Y. K.

1995-03-01

116

Giddings Austin chalk enters deep lean-gas phase  

SciTech Connect

Deep lean gas is the latest phase in the growth of the Giddings field Austin chalk play. The first phase involved drilling vertical oil and gas wells. Next came the horizontal well boom in the shallower Austin chalk area, which is still continuing. And now this third phase places horizontal laterals in the Austen chalk at about 14,000--15,000 ft to produce lean gas. The article describes the producing wells and gas gathering.

Moritis, G.

1995-12-25

117

Dimers in nucleating vapors  

NASA Astrophysics Data System (ADS)

The dimer stage of nucleation may affect considerably the rate of the nucleation process at high supersaturation of the nucleating vapor. Assuming that the dimer formation limits the nucleation rate, the kinetics of the particle formation-growth process is studied starting with the definition of dimers as bound states of two associating molecules. The partition function of dimer states is calculated by summing the Boltzmann factor over all classical bound states, and the equilibrium population of dimers is found for two types of intermolecular forces: the Lennard-Jones (LJ) and rectangular well+hard core (RW) potentials. The principle of detailed balance is used for calculating the evaporation rate of dimers. The kinetics of the particle formation-growth process is then investigated under the assumption that the trimers are stable with respect to evaporation and that the condensation rate is a power function of the particle mass. If the power exponent ?=n/(n+1) (n is a non-negative integer), the kinetics of the process is described by a finite set of moments of particle mass distribution. When the characteristic time of the particle formation by nucleation is much shorter than that of the condensational growth, n+2 universal functions of a nondimensional time define the kinetic process. These functions are calculated for ?=2/3 (gas-to-particle conversion in the free molecular regime) and ?=1/2 (formation of islands on surfaces).

Lushnikov, A. A.; Kulmala, M.

1998-09-01

118

Gas-phase fragmentation of polyoxotungstate anions.  

PubMed

A series of phospho-polyoxotungstate anions was transferred to the gas phase via electrospray ionization (ESI), and the anions' fragmentation was examined by collision-induced dissociation (CID). The anions included [PW12O40]3-, [P2W18O62]6-, and {Co4(H2O)2][PW9O34]2}10- as well as lacunary and metal-substituted derivatives such as [PW11O39]7- and [MPW11O39]5- (M = Co(II), Ni(II), Cu(II)). Common species observed in the mass spectra arose from protonation and alkali metal cationization of the precursor ions. Additional species arising from the formal loss of oxide from the precursor species were also observed, presumably formed via protonation and the loss of an oxo ligand as water. These processes of protonation/cationization and the loss of water both led to species with reduced gas-phase anionic charges, and their formation appears to be driven by the enhanced effects of Coulombic repulsion in the desolvated species generated during transfer to the gas phase via ESI. Fragmentation of selected species was examined by multistage mass spectrometry experiments employing CID. Fragmentation occurred via multiple reaction channels, leading to pairs of complementary product anions whose total stoichiometry and charge matched those of the precursor anion. For example, [PW12O40]3- fragmented to give pairs of product ions of general formulas [W(x)O(3x+1)]2- and [PW(12-x)O(39-3x)]- (x = 6-9), with the most intense pair being [W6O19]2- and [PW6O21]-. Similar ions were also observed for fragmentation of [P2W18O61]4- (derived from the loss of water from [P2W18O62]6-). The lacunary and M(II)-substituted lacunary systems fragmented via related pathways, with the latter generating additional fragment ions due to the presence of M(II). These results highlight the usefulness of ESI-MS in the characterization of complex polyoxometalate anion clusters. PMID:19072590

Ma, Michelle T; Waters, Tom; Beyer, Karin; Palamarczuk, Rosemary; Richardt, Peter J S; O'Hair, Richard A J; Wedd, Anthony G

2009-01-19

119

Assembling gas-phase reaction mechanisms for high temperature inorganic systems based on quantum chemistry calculations and reaction rate theories  

NASA Astrophysics Data System (ADS)

Detailed chemical kinetic modeling based on computational quantum chemistry has been quite successful in making quantitative predictions about some systems, particularly the combustion of small hydrocarbons and certain areas of atmospheric chemistry. The gas phase chemistry of many processes in high-temperature inorganic systems, from materials synthesis to propulsion to waste incineration, could in principle be modeled with equal or greater success using detailed chemical kinetic modeling. This contribution provides examples from our own work of how computational quantum chemistry can be used in developing gas phase reaction mechanisms for modeling of high temperature materials processing. In the context of CVD of silicon from dichlorosilane, CVD of alumina from AlCl3/H2/CO2 mixtures, and particle nucleation from silane, this detailed chemical kinetic modeling has given us insight into gas phase reaction pathways that we would not likely have gained by other means.

Swihart, Mark T.

2005-02-01

120

Gas-phase thermochemistry of chloropyridines  

NASA Astrophysics Data System (ADS)

The gas-phase standard molar enthalpy of formation of the 2,3,5-trichloropyridine compound was derived from the enthalpies of combustion of the crystalline solid measured by rotating-bomb calorimetry and its enthalpy of sublimation obtained by Calvet microcalorimetry at T = 298.15 K. The standard enthalpies of formation for this compound and for the other chlorosubstituted pyridines were determined by DFT calculations. The experimental enthalpy of formation of 2,3,5-trichloropyridine is (65.8 ± 2.3) kJ mol -1, in excellent agreement with the B3LYP/6-311+G(2d,2p)//B3LYP/6-31G(d) value. The affinity of pyridine to some metal cations was also calculated at the same DFT level of theory and compared with experimental data.

Gomes, José R. B.; Amaral, Luísa M. P. F.; Ribeiro da Silva, Manuel A. V.

2005-04-01

121

Phase transitions in a gas of anyons  

SciTech Connect

We continue our numerical Monte Carlo simulation of a gas of closed loops on a 3 dimensional lattice, however, now in the presence of a topological term added to the action which corresponds to the total linking number between the loops. We compute the linking number using a novel approach employing certain notions from knot theory. Adding the topological term converts the particles into anyons. Interpreting the model as an effective theory that describes the 2+1-dimensional Abelian Higgs model in the asymptotic strong-coupling regime, the topological linking number simply corresponds to the addition to the action of the Chern-Simons term. The system continues to exhibit a phase transition as a function of the vortex mass as it becomes small. We find the following new results. The Chern-Simons term has no effect on the Wilson loop. On the other hand, it does effect the 't Hooft loop of a given configuration, adding the linking number of the 't Hooft loop with all of the dynamical vortex loops. We find the unexpected result that both the Wilson loop and the 't Hooft loop exhibit a perimeter law even though there are no massless particles in the theory, in both phases of the theory. It should be noted that our method suffers from numerical instabilities if the coefficient of the Chern-Simons term is too large; thus, we have restricted our results to small values of this parameter. Furthermore, interpreting the lattice loop gas as an effective theory describing the Abelian Higgs model is only known to be true in the infinite coupling limit; for strong but finite coupling this correspondence is only a conjecture, the validity of which is beyond the scope of this article.

MacKenzie, R.; Nebia-Rahal, F.; Paranjape, M. B. [Groupe de physique des particules, Departement de physique, Universite de Montreal, C.P. 6128, Succ. Centre-ville, Montreal, Quebec, H3C 3J7 (Canada); Richer, J. [Reseau quebecois de calcul de haute performance, DGTIC, Universite de Montreal, C.P. 6128, Succ. Centre-ville, Montreal, Quebec, H3C 3J7 (Canada)

2010-10-01

122

Transferring pharmaceuticals into the gas phase  

NASA Astrophysics Data System (ADS)

The dissolution of molecules of biological interest in supercritical carbon dioxide is investigated using pulsed molecular beam mass spectrometry. Due to the mild processing temperatures of most supercritical fluids, their adiabatic expansion into vacuum permits to transfer even thermally very sensitive substances into the gas phase, which is particularly attractive for pharmaceutical and biomedical applications. In addition, supercritical CO2constitutes a chemically inert solvent that is compatible with hydrocarbon-free ultrahigh vacuum conditions. Here, we report on the dissolution and pulsed supersonic jet expansion of caffeine (C8H10N4O2), the provitamin menadione (C11H8O2), and the amino acid derivative l-phenylalanine tert-butyl ester hydrochloride (C6H5CH2CH(NH2)COOC(CH3)3[dot operator]HCl), into vacuum. An on-axis residual gas analyzer is used to monitor the relative amounts of solute and solvent in the molecular beam as a function of solvent densityE The excellent selectivity and sensitivity provided by mass spectrometry permits to probe even trace amounts of solutes. The strong density variation of CO2 close to the critical point results in a pronounced pressure dependence of the relative ion currents of solute and solvent molecules, reflecting a substantial change in solubility.

Christen, Wolfgang; Krause, Tim; Rademann, Klaus

2008-11-01

123

The VRT gas turbine combustor - Phase II  

NASA Technical Reports Server (NTRS)

An innovative annular combustor configuration is being developed for aircraft and other gas turbine engines. This design has the potential of permitting higher turbine inlet temperatures by reducing the pattern factor and providing a major reduction in NO(x) emission. The design concept is based on a Variable Residence Time (VRT) technique which allows large fuel particles adequate time to completely burn in the circumferentially mixed primary zone. High durability of the combustor is achieved by dual-function use of the incoming air. In Phase I, the feasibility of the concept was demonstrated by water analogue tests and 3D computer modeling. The flow pattern within the combustor was as predicted. The VRT combustor uses only half the number of fuel nozzles of the conventional configuration. In Phase II, hardware was designed, procured, and tested under conditions simulating typical supersonic civil aircraft cruise conditions to the limits of the rig. The test results confirmed many of the superior performance predictions of the VRT concept. The Hastelloy X liner showed no signs of distress after nearly six hours of tests using JP5 fuel.

Melconian, Jerry O.; Mongia, Hukam C.; Nguyen, Hung L.

1992-01-01

124

On Immersion Freezing as a Nucleation Mechanism in Mixed-Phase Stratus Gijs de Boer, Tempei Hashino,Gregory J.Tripoli and Edwin W.Eloranta  

E-print Network

courtesy of J.P.Blanchet (From Bigg,1980) - Bigg (1980) observed sulfuric acid coating on aero- sol particl,condensation and deposi- tion freezing are not primarily responsible for ice production, as all require free Nucleation Contact Nucleation Depositional Nucleation Immersion Nucleation So which one drives ice production

Eloranta, Edwin W.

125

Nucleation in the presence of long-range interactions. [performed on ferroelectric barium titanate  

NASA Technical Reports Server (NTRS)

Unlike droplet nucleation near a liquid-gas critical point, the decay of metastable phases in crystalline materials is strongly affected by the presence of long-range forces. Field quench experiments performed on the ferroelectric barium titanate indicate that nucleation in this material is markedly different from that observed in liquids. In this paper, a theory for nucleation at a first-order phase transition in which the mediating forces are long range is presented. It is found that the long-range force induces cooperative nucleation and growth processes, and that this feedback mechanism produces a well-defined delay time with a sharp onset in the transformation to the stable phase. Closed-form expressions for the characteristic onset time and width of the transition are developed, in good agreement with numerical and experimental results.

Chandra, P.

1989-01-01

126

Homogeneous bubble nucleation in rhyolitic melt: Experiments and nonclassical theory  

NASA Astrophysics Data System (ADS)

The transfer of volatiles from the Earth's interior to the atmosphere occurs through degassing of magma, the dynamics of which assert a significant control on volcanic eruptions. The first and most critical step in degassing is the nucleation of gas bubbles, which requires that a sufficient number of volatile molecules cluster together to overcome the free energy associated with the formation of a new interface between nucleus and surrounding melt. This free energy is a function of surface tension, typically assumed to equate to the macroscopically measurable value. Surface tension estimates inferred from bubble nucleation experiments in silicate melts are, however, lower than direct macroscopic measurements, making it difficult to accurately predict magma ascent and decompression rates from measured bubble number densities in pyroclasts. We provide a potential resolution to this problem through an integrated study of bubble nucleation experiments and modeling thereof, based on nonclassical nucleation theory. We find that surface tension between critical bubble nuclei and the surrounding melt depends on the degree of supersaturation and is lower than the macroscopically measured value. This is consistent with the view that far from equilibrium the interface between a nucleus and surrounding metastable bulk phase is diffuse instead of sharp. As a consequence, the increase in nucleation rate with supersaturation is significantly larger at high supersaturations than predicted by classical nucleation theory.

Gonnermann, H. M.; Gardner, J. E.

2013-11-01

127

Single Particle Laser Mass Spectrometry Applied to Differential Ice Nucleation Experiments at the AIDA Chamber  

SciTech Connect

Experiments conducted at the Aerosol Interactions and Dynamics in the Atmosphere (AIDA) chamber located in Karlsruhe, Germany permit investigation of particle properties that affect the nucleation of ice at temperature and water vapor conditions relevant to cloud microphysics and climate issues. Ice clouds were generated by heterogeneous nucleation of Arizona test dust (ATD), illite, and hematite and homogeneous nucleation of sulfuric acid. Ice crystals formed in the chamber were inertially separated from unactivated, or ‘interstitial’ aerosol particles with a pumped counterflow virtual impactor (PCVI), then evaporated. The ice residue (i.e., the aerosol which initiated ice nucleation plus any material which was scavenged from the gas- and/or particle-phase), was chemically characterized at the single particle level using a laser ionization mass spectrometer. In this manner the species that first nucleated ice could be identified out of a mixed aerosol population in the chamber. Bare mineral dust particles were more effective ice nuclei (IN) than similar particles with a coating. Metallic particles from contamination in the chamber initiated ice nucleation before other species but there were few enough that they did not compromise the experiments. Nitrate, sulfate, and organics were often detected on particles and ice residue, evidently from scavenging of trace gas-phase species in the chamber. Hematite was a more effective ice nucleus than illite. Ice residue was frequently larger than unactivated test aerosol due to the formation of aggregates due to scavenging, condensation of contaminant gases, and the predominance of larger aerosol in nucleation.

Gallavardin, S. J.; Froyd, Karl D.; Lohmann, U.; Moehler, Ottmar; Murphy, Daniel M.; Cziczo, Dan

2008-08-26

128

Spaceborne lidar observations of the ice-nucleating potential of dust, polluted dust, and smoke aerosols in mixed-phase clouds  

NASA Astrophysics Data System (ADS)

Previous laboratory studies and in situ measurements have shown that dust particles possess the ability to nucleate ice crystals, and smoke particles to some extent as well. Even with coatings of pollutants such as sulphate and nitrate on the surface of dust particles, it has been shown that polluted dust particles are still able to nucleate ice in the immersion, deposition, condensation, and contact freezing modes, albeit less efficiently than unpolluted dust. The ability of these aerosols to act as ice nuclei in the Earth's atmosphere has important implications for the Earth's radiative budget and hence global climate change. Here we determine the relationship between cloud thermodynamic phase and dust, polluted dust, and smoke aerosols individually by analyzing their vertical profiles over a ˜5 year period obtained by NASA's spaceborne lidar, Cloud-Aerosol Lidar with Orthogonal Polarization. We found that when comparing the effects of temperature and aerosols, temperature appears to have the dominant influence on supercooled liquid cloud fraction. Nonetheless, we found that aerosols still appear to exert a strong influence on supercooled liquid cloud fraction as suggested by the existence of negative temporal and spatial correlations between supercooled liquid cloud fraction and frequencies of dust aerosols from around the world, at the -10°C, -15°C, -20°C, and -25°C isotherms. Although smoke aerosol frequencies were also found to be negatively correlated with supercooled liquid cloud fraction, their correlations are weaker in comparison to those between dust frequencies and supercooled liquid cloud fraction. For the first time, we show this based on observations from space, which lends support to previous studies that dust and potentially smoke aerosols can globally alter supercooled liquid cloud fraction. Our results suggest that the ice-nucleating ability of these aerosols may have an indirect climatic impact that goes beyond the regional scale, by influencing cloud thermodynamic phase globally.

Tan, Ivy; Storelvmo, Trude; Choi, Yong-Sang

2014-06-01

129

Liquid-Liquid Transition at Tg and Stable-Glass Phase Nucleation Rate Maximum at the Kauzmann Temperature TK  

E-print Network

An undercooled liquid is unstable. The driving force of the glass transition at Tg is a change of the undercooled-liquid Gibbs free energy. The classical Gibbs free energy change for a crystal formation is completed including an enthalpy saving. The crystal growth critical nucleus is used as a probe to observe the Laplace pressure change Dp accompanying the enthalpy change -Vm*Dp at Tg where Vm is the molar volume. A stable glass-liquid transition model predicts the specific heat jump of fragile liquids at temperatures smaller than Tg, the Kauzmann temperature TK where the liquid entropy excess with regard to crystal goes to zero, the equilibrium enthalpy between TK and Tg, the maximum nucleation rate at TK of superclusters containing magic atom numbers, and the equilibrium latent heats at Tg and TK. Strong-to-fragile and strong-to-strong liquid transitions at Tg are also described and all their thermodynamic parameters are determined from their specific heat jumps. The existence of fragile liquids quenched in the amorphous state, which do not undergo liquid-liquid transition during heating preceding their crystallization, is predicted. Long ageing times leading to the formation at TK of a stable glass composed of superclusters containing up to 147 atoms, touching and interpenetrating, are evaluated from nucleation rates.

Robert Felix Tournier

2014-04-10

130

Gas-Liquid Flows and Phase Separation  

NASA Technical Reports Server (NTRS)

Common issues for space system designers include:Ability to Verify Performance in Normal Gravity prior to Deployment; System Stability; Phase Accumulation & Shedding; Phase Separation; Flow Distribution through Tees & Manifolds Boiling Crisis; Heat Transfer Coefficient; and Pressure Drop.The report concludes:Guidance similar to "A design that operates in a single phase is less complex than a design that has two-phase flow" is not always true considering the amount of effort spent on pressurizing, subcooling and phase separators to ensure single phase operation. While there is still much to learn about two-phase flow in reduced gravity, we have a good start. Focus now needs to be directed more towards system level problems .

McQuillen, John

2004-01-01

131

Nucleation of ice and its management in ecosystems.  

PubMed

In addition to the gas and liquid phases, water can exist in many different solid states. Some of these are the well-studied crystalline ice polymorphs and the clathrate hydrates, but at least two distinguishable amorphous solid forms have also been shown to exist. This diversity of possible condensed states implies a multiplicity of transitions, each of them presumably associated with a nucleation step. Disagreement still exists as to whether the amorphous states can be regarded as metastable phases, and whether the phenomenon of polyamorphism can be treated in terms of phase transitions. In the Earth's hydrosphere, several of the crystalline and amorphous water phases can be formed from vapour, under given conditions of temperature, pressure and supersaturation, and classical nucleation theory is believed to account reasonably well for the observed growth of condensed forms of water in the upper atmosphere. Many terrestrial organisms are able to activate mechanisms to control the nucleation and growth of ice when exposed to sub-zero temperatures, thus enabling them to minimize the lethal effects of extreme freeze desiccation. The substances involved in these mechanisms include carbohydrates, amino acids and so-called cold-shock proteins, but the actual mechanisms of interfering with ice nucleation, although quite well documented, are as yet imperfectly understood. This is particularly true for the genetic control associated with biochemical processes that produce freeze resistance and freeze tolerance. The molecular biology of cold stress is currently a subject of intensive study. PMID:12662454

Franks, Felix

2003-03-15

132

Quantum control of I2 in the gas phase and in condensed phase solid Kr matrix  

E-print Network

into account using both exact quantum dynamics and nearly classical theory. For the condensed phase, since control is indeed possible in con- densed phases. There are two paradigms for quantum control: a dynamicQuantum control of I2 in the gas phase and in condensed phase solid Kr matrix Christopher J

Apkarian, V. Ara

133

Absorption of Gas Phase Contaminant Mixtures.  

National Technical Information Service (NTIS)

This project seeks to study the effect of multiple gas-vapor mixtures on the activated carbon adsorption breakthrough time and pattern. Activated carbon cartridges used for respiratory protection are tested in most cases for a single component at relative...

C. Lungu

2004-01-01

134

Gas-Phase Spectroscopy of Biomolecular Building Blocks  

NASA Astrophysics Data System (ADS)

Gas-phase spectroscopy lends itself ideally to the study of isolated molecules and provides important data for comparison with theory. In recent years, we have seen enormous progress in the study of biomolecular building blocks in the gas phase. The motivation for such work is threefold: (a) It is important to distinguish between intrinsic molecular properties and properties that result from the biological environment. (b) Gas-phase spectroscopy of clusters provides insights into fundamental interactions and into microsolvation. (c) Gas-phase data support quantum-chemical calculations. This review focuses on the current status of (poly)amino acids and DNA bases. Recent results help elucidate structure and hydrogen-bonded interactions, as well as showcase a successful interplay between theory and experiment.

de Vries, Mattanjah S.; Hobza, Pavel

2007-05-01

135

Mixed Stationary Liquid Phases for Gas-Liquid Chromatography.  

ERIC Educational Resources Information Center

Describes a laboratory technique for use in an undergraduate instrumental analysis course that, using the interpretation of window diagrams, prepares a mixed liquid phase column for gas-liquid chromatography. A detailed procedure is provided. (BT)

Koury, Albert M.; Parcher, Jon F.

1979-01-01

136

Fission and Nuclear Liquid-Gas Phase Transition  

E-print Network

The temperature dependence of the liquid-drop fission barrier is considered, the critical temperature for the liquid-gas phase transition in nuclear matter being a parameter. Experimental and calculated data on the fission probability are compared for highly excited $^{188}$Os. The calculations have been made in the framework of the statistical model. It is concluded that the critical temperature for the nuclear liquid--gas phase transition is higher than 16 MeV.

E. A. Cherepanov; V. A. Karnaukhov

2007-03-30

137

The gas phase oxidation of elemental mercury by ozone  

Microsoft Academic Search

The gas phase reaction between elemental mercury (Hg0) and ozone (03) has been studied in sunlight, in darkness, at different temperatures, and different surface-to-volume (s\\/v) ratios. At 03 concentrations above 20 ppm, a loss of Hg0 and a simultaneous formation of oxidized mercury (Hg(II)) was observed. The results suggest a partly heterogeneous reaction, with a gas phase rate constant of

B. Hall

1995-01-01

138

Photodesorption of ices Releasing organic precursors into the gas phase  

Microsoft Academic Search

A long-standing problem in interstellar chemistry is how molecules can be maintained in the gas phase at the extremely low temperatures in space. Photodesorption has been suggested to explain the observed cold gas in cloud cores and disk mid-planes. We are studying the UV photodesorption of ices experimentally under ultra high vacuum and at astrochemically relevant temperatures (15 27 K)

Karin I. Öberg; Ewine F. van Dishoeck; Harold Linnartz

2008-01-01

139

High resolution ion mobility measurements for gas phase proteins: correlation between solution phase and gas phase conformations  

NASA Astrophysics Data System (ADS)

Our high resolution ion mobility apparatus has been modified by attaching an electrospray source to perform measurements for biological molecules. While the greater resolving power permits the resolution of more conformations for BPTI and cytochrome c, the resolved features are generally much broader than expected for a single rigid conformation. A major advantage of the new experimental configuration is the much gentler introduction of ions into the drift tube, so that the observed gas phase conformations appear to more closely reflect those present in solution. For example, it is possible to distinguish between the native state of cytochrome c and the methanol-denatured form on the basis of the ion mobility measurements; the mass spectra alone are not sensitive enough to detect this change. Thus this approach may provide a quick and sensitive tool for probing the solution phase conformations of biological molecules.

Hudgins, Robert R.; Woenckhaus, Jürgen; Jarrold, Martin F.

1997-11-01

140

Ice Nucleation by High Molecular Weight Organic Compounds  

NASA Astrophysics Data System (ADS)

Deep convection in the tropics is frequently associated with biomass burning. Recent work has suggested that the size of ice crystals in the anvils of tropical cumulonimbus clouds may be affected by biomass burning, though the mechanism for such an effect is uncertain (Sherwood, 2002). We will present results of an investigation of the role that high molecular weight organic compounds, known to be produced in biomass burning (Elias et al., 1999), may play in tropical cirrus anvils through heterogeneous nucleation of ice. In particular, we examine the mechanisms underlying heterogeneous nucleation of ice by films of long chain alcohols by studying the interaction of the alcohols and water/ice using temperature controlled, Attenuated Total Reflection - Fourier Transform Infrared spectroscopy. The mechanisms are interpreted in the context of recent criticisms of some aspects of classical nucleation theory (Seeley and Seidler, 2001; Oxtoby, 1998). References V. Elias, B. Simoneit, A. Pereira, J. Cabral, and J. Cardoso, Detection of high molecular weight organic tracers in vegetation smoke samples by high-temperature gas chromatography-mass spectrometry. Environ. Sci. Tecnol., 33, 2369-2376, 1999. D. Oxtoby, Nucleation of first-order phase transitions. Acc. Chem. Res., 31, 91-97, 1998. L. Seeley and G. Seidler, Preactivation in the nucleation of ice by Langmuir films of aliphatic alcohols. J. Chem. Phys., 114, 10464-10470, 2001. S. Sherwood, Aerosols and ice particle size in tropical cumulonimbus. J. Climate, 15, 1051-1063, 2002.

Cantrell, W.

2003-12-01

141

Thermodynamic and kinetic consistency of calculated binary nucleation rates  

SciTech Connect

To establish the accuracy and applicability of analytical expressions for the steady state rate of binary nucleation, we numerically solved the birth-death equations for the vapor-to-liquid transition. These calculations were performed using rate coefficients that are consistent with the principle of detailed balance and a new self-consistent form of the equilibrium distribution function for binary cluster concentrations. We found that the customary saddle point and growth path approximations are almost always valid and can fail only if the nucleating solution phase is significantly nonideal. For example, problems can arise when the vapor composition puts the system on the verge of partial liquid phase miscibility. When this occurs for comparable monomer impingement rates, nucleation still occurs through the saddle point, but the usual quadratic expansion for the cluster free energy is inadequate. When the two impingement rates differ significantly, however, the major particle flux may bypass the saddle point and cross a low ridge on the free energy surface. The dependence of the saddle point location on the gas phase composition is also important in initiating or terminating ridge crossing nucleation.

Wilemski, G. [Lawrence Livermore National Lab., CA (United States); Wyslouzil, B.E. [Worcester Polytechnic Institute, MA (United States)

1996-04-02

142

Vaccum Gas Tungsten Arc Welding, phase 1  

Microsoft Academic Search

This two year program will investigate Vacuum Gas Tungsten Arc Welding (VGTAW) as a method to modify or improve the weldability of normally difficult-to-weld materials. VGTAW appears to offer a significant improvement in weldability because of the clean environment and lower heat input needed. The overall objective of the program is to develop the VGTAW technology and implement it into

P. D. Krotz; D. T. Todd; Y. K. Liaw

1995-01-01

143

Experimental investigation and modeling of diamond nucleation on silica substrates  

NASA Astrophysics Data System (ADS)

Thin films created using chemical vapor deposition (CVD) have numerous applications. In order for these films to function effectively it is often necessary to better control their properties. This can be accomplished through a more thorough understanding of the initial stages of a film's growth. At this stage, when nucleation occurs, the microstructure of a film is determined and this has a significant influence on its properties. Two materials which are currently grown using CVD are diamond and silicon nitride. In this research, an investigation of the nucleation of both of these materials is conducted. Deposition of diamond was carried out with a microwave plasma system, while silicon nitride was nucleated using an impinging-jet reactor. Several characterization techniques were employed, including scanning electron microscopy (SEM), transmission electron microscopy (TEM), parallel electron energy loss spectroscopy (PEELS) and optical emission spectroscopy (OES). The primary focus of the work was on diamond nucleation. Deposition was conducted on three different substrates, including silicon, oxidized silicon and silica. Several differences in experimental results were observed between the substrates. In order to explain these variations a kinetic model was developed which considers the influence of the substrate on the local gas phase chemistry. The model reveals that the concentration of oxygen is greater near silica substrates. TEM and PEELS show the presence of amorphous carbon islands on silica substrates after a pretreatment step. It is probable that these serve as nucleation sites for crystalline diamond. An additional kinetic model was developed which considers the islands as mixtures of spsp2 and spsp3 carbon. It was found that the lower surface energy of graphite and higher supersaturation ratio of diamond lead to an enhancement of nucleation. Silicon nitride was deposited on an interlayer that was found to consist of amorphous silicon nitride and crystalline silicon. The structure of the interlayer changed as it was deposited until eventually nucleation of crystalline Sisb3Nsb4 became favorable.

Koritala, Rachel Elizabeth

1997-08-01

144

Nucleation stage in supersaturated vapor with inhomogeneities due to nonstationary diffusion onto growing droplets  

NASA Astrophysics Data System (ADS)

An analytical description of the nucleation stage in a supersaturated vapor with instantly created supersaturation is given with taking into account the vapor concentration inhomogeneities arising as a result of depletion due to nonstationary diffusion onto growing droplets. This description is based on the fact, that the intensity of the nucleation of new droplets is suppressed in spherical diffusion regions of a certain size surrounding previously nucleated droplets, and remains at the initial level in the remaining volume of the vapor-gas medium. The value of the excluded volume (excluded from nucleation) depends on the explicit form of the vapor concentration profile in the space around the growing droplet, and we use for that the unsteady self-similar solution of the time-dependent diffusion equation with a convective term describing the flow of the gas-vapor mixture caused by the moving surface of the single growing droplet. The main characteristics of the phase transition at the end of the nucleation stage are found and compared with those in the theory of nucleation with homogeneous vapor consumption (the theory of mean-field vapor supersaturation). It is shown that applicability of the mean-field approach depends on smallness of the square root of the ratio of the densities of metastable and stable phases. With increasing the temperature of the supersaturated vapor or for liquid or solid solutions, this smallness weakens, and then it would be more correct to use the excluded volume approach.

Kuchma, Anatoly; Markov, Maxim; Shchekin, Alexander

2014-05-01

145

Nucleation and Coalescence of Indium Rich InGaN Layers on Nitridated Sapphire in Metal-Organic Vapor Phase Epitaxy  

NASA Astrophysics Data System (ADS)

We report on the evolution of N-polar wurtzite (000bar 1) InGaN layers with high indium content grown directly on nitridated (0001) sapphire by metal-organic vapor phase epitaxy. In-situ ellipsometry showed an initial growth delay of 5-8 nm for layers with more than 45% indium content. Atomic force microscopy showed small dense islands which reached their final size after 5-8 nm deposition. The roughness saturated only after 15 nm, and the width of the X-ray diffraction (00.2) reflex showed a similar behavior. Therefore, N-polar InGaN grows via nucleation (d < 10 nm) followed by coalescence (d < 20 nm). With less than 40% indium the coalescence is much slower, very similar to Ga-polar (0001) GaN despite N-polarity of the InN layers. This indicates towards a surface transition between 40 and 50% indium content.

Dinh, Duc V.; Solopow, Sergej; Pristovsek, Markus; Kneissl, Michael

2013-08-01

146

Gas phase acetaldehyde production in a continuous bioreactor  

SciTech Connect

The gas phase continuous production of acetaldehyde was studied with particular emphasis on the development of biocatalyst (alcohol oxidase on solid phase support materials) for a fixed bed reactor. Based on the experimental results in a batch bioreactor, the biocatalysts were prepared by immobilization of alcohol oxidase on Amberlite IRA-400, packed into a column, and the continuous acetaldehyde production in the gas phase by alcohol oxidase was performed. The effects of the reaction temperature, flow rates of gaseous stream, and ethanol vapor concentration on the performance of the continuous bioreactor were investigated.

Hwang, Soon Ook (Northeastern Univ., Boston, MA (United States). Dept. of Chemical Engineering); Trantolo, D.J. (Northeastern Univ., Boston, MA (United States). Center for Biotechnology Engineering); Wise, D.L. (Northeastern Univ., Boston, MA (United States). Dept. of Chemical Engineering Northeastern Univ., Boston, MA (United States). Center for Biotechnology Engineering)

1993-08-20

147

Simulation Approach for Microscale Noncontinuum Gas-Phase Heat Transfer  

NASA Astrophysics Data System (ADS)

In microscale thermal actuators, gas-phase heat transfer from the heated beams to the adjacent unheated substrate is often the main energy-loss mechanism. Since the beam-substrate gap is comparable to the molecular mean free path, noncontinuum gas effects are important. A simulation approach is presented in which gas-phase heat transfer is described by Fourier's law in the bulk gas and by a wall boundary condition that equates the normal heat flux to the product of the gas-solid temperature difference and a heat transfer coefficient. The dimensionless parameters in this heat transfer coefficient are determined by comparison to Direct Simulation Monte Carlo (DSMC) results for heat transfer from beams of rectangular cross section to the substrate at free-molecular to near-continuum gas pressures. This simulation approach produces reasonably accurate gas-phase heat-transfer results for wide ranges of beam geometries and gas pressures. Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.

Torczynski, J. R.; Gallis, M. A.

2008-11-01

148

Para-Hydrogen-Enhanced Gas-Phase Magnetic Resonance Imaging  

SciTech Connect

Herein, we demonstrate magnetic resonance imaging (MRI) inthe gas phase using para-hydrogen (p-H2)-induced polarization. A reactantmixture of H2 enriched in the paraspin state and propylene gas is flowedthrough a reactor cell containing a heterogenized catalyst, Wilkinson'scatalyst immobilized on modified silica gel. The hydrogenation product,propane gas, is transferred to the NMR magnet and is spin-polarized as aresult of the ALTADENA (adiabatic longitudinal transport and dissociationengenders net alignment) effect. A polarization enhancement factor of 300relative to thermally polarized gas was observed in 1D1H NMR spectra.Enhancement was also evident in the magnetic resonance images. This isthe first demonstration of imaging a hyperpolarized gaseous productformed in a hydrogenation reaction catalyzed by a supported catalyst.This result may lead to several important applications, includingflow-through porous materials, gas-phase reaction kinetics and adsorptionstudies, and MRI in low fields, all using catalyst-free polarizedfluids.

Bouchard, Louis-S.; Kovtunov, Kirill V.; Burt, Scott R.; Anwar,M. Sabieh; Koptyug, Igor V.; Sagdeev, Renad Z.; Pines, Alexander

2007-02-23

149

Gas-phase diffusion in porous media: Comparison of models  

SciTech Connect

Two models are commonly used to analyze gas-phase diffusion in porous media in the presence of advection, the Advective-Dispersive Model (ADM) and the Dusty-gas Model (DGM). The ADM, which is used in TOUGH2, is based on a simple linear addition of advection calculated by Darcy`s law and ordinary diffusion using Fick`s law with a porosity-tortuosity-gas saturation multiplier to account for the porous medium. Another approach for gas-phase transport in porous media is the Dusty-Gas Model. This model applies the kinetic theory of gases to the gaseous components and the porous media (or dust) to combine transport due to diffusion and advection that includes porous medium effects. The two approaches are compared in this paper.

Webb, S.W.

1998-09-01

150

Molecular Dynamics of Simulation of the Nucleation, Growth, Inhibition and Control of Gas Hydrates. Annual Report, March 1992-June 1993.  

National Technical Information Service (NTIS)

This is the second year of a three-year project using molecular simulation techniques tailored specifically for the determination of early-stage kinetics of natural gas hydrate crystal growth and dissolution. This year, extensive simulations of the kineti...

P. Clancy

1993-01-01

151

Communication: Fourier-transform infrared probing of remarkable quantities of gas trapped in cold homogeneously nucleated nanodroplets  

NASA Astrophysics Data System (ADS)

Studies of catalyzed all-vapor gas-hydrate formation on a sub-second timescale have been extended with a special focus on liquid-droplet compositions at the instant of hydrate crystallization. This focus has been enabled by inclusion of methanol in the all-vapor mixture. This slows droplet to gas-hydrate conversion near 200 K to a time scale suited for standard FTIR sampling. Such droplet data are sought as a guide to ongoing efforts to reduce the amount of guest catalyst required for instant formation of the gas hydrates. For the same reason, all-vapor sampling has also been extended to the generation of long-lived liquid droplets with reduced or no water content. Observations of single-solvent droplets show that surprising quantities of gas molecules are trapped during rapid droplet growth. For example, CO2 is trapped at levels near 50 mol. % in droplets of acetone, tetrahydrofuran, or trimethylene oxide formed under CO2 pressures of several Torr in a cold-chamber at 170 K. Less but significant amounts of gas are trapped at higher temperatures, or in methanol or water-methanol droplets. The droplet metastability appears to commonly lead to formation of bubbles larger than the original nanodroplets. Besides serving as a guide for the all-vapor gas-hydrate studies, the semiquantitative evidence of extensive trapping of gases is expected to have a role in future studies of atmospheric aerosols.

Uras-Aytemiz, Nevin; Devlin, J. Paul

2013-07-01

152

Hydrodynamic and gas phase axial dispersion in an air-molten salt two-phase system (molten salt oxidation reactor)  

Microsoft Academic Search

The effects of the gas velocity (0.05–0.22m\\/s) and temperature (870–970°C) on the gas holdup and the gas phase axial dispersion coefficient have been studied in a molten salt oxidation reactor (0.076m i.d.×0.653m H., air-molten sodium carbonate salt two-phase system). The gas phase holdup and the amount of the axial gas phase dispersion coefficient were experimentally evaluated by means of the

Yong-Jun Cho; Hee-Chul Yang; Hee-Chul Eun; Jae-Hyung Yoo; Joon-Hyung Kim

2005-01-01

153

Microfabricated Gas Phase Chemical Analysis Systems  

SciTech Connect

A portable, autonomous, hand-held chemical laboratory ({mu}ChemLab{trademark}) is being developed for trace detection (ppb) of chemical warfare (CW) agents and explosives in real-world environments containing high concentrations of interfering compounds. Microfabrication is utilized to provide miniature, low-power components that are characterized by rapid, sensitive and selective response. Sensitivity and selectivity are enhanced using two parallel analysis channels, each containing the sequential connection of a front-end sample collector/concentrator, a gas chromatographic (GC) separator, and a surface acoustic wave (SAW) detector. Component design and fabrication and system performance are described.

Casalnuovo, Stephen A.; Frye-Mason, Gregory C; Heller, Edwin J.; Hietala, Vincent M.; Kottenstette, Richard J.; Lewis, Patrick R.; Manginell, Ronald P.; Matzke, Carolyn M.; Wong, C. Channy

1999-08-02

154

Microfabricated Gas Phase Chemical Analysis Systems  

SciTech Connect

A portable, autonomous, hand-held chemical laboratory ({micro}ChemLab{trademark}) is being developed for trace detection (ppb) of chemical warfare (CW) agents and explosives in real-world environments containing high concentrations of interfering compounds. Microfabrication is utilized to provide miniature, low-power components that are characterized by rapid, sensitive and selective response. Sensitivity and selectivity are enhanced using two parallel analysis channels, each containing the sequential connection of a front-end sample collector/concentrator, a gas chromatographic (GC) separator, and a surface acoustic wave (SAW) detector. Component design and fabrication and system performance are described.

FRYE-MASON,GREGORY CHARLES; HELLER,EDWIN J.; HIETALA,VINCENT M.; KOTTENSTETTE,RICHARD; LEWIS,PATRICK R.; MANGINELL,RONALD P.; MATZKE,CAROLYN M.; WONG,CHUNGNIN C.

1999-09-16

155

Experiments on Nucleation in Different Flow Regimes  

NASA Technical Reports Server (NTRS)

The vast majority of metallic engineering materials are solidified from the liquid phase. Understanding the solidification process is essential to control microstructure, which in turn, determines the properties of materials. The genesis of solidification is nucleation, where the first stable solid forms from the liquid phase. Nucleation kinetics determine the degree of undercooling and phase selection. As such, it is important to understand nucleation phenomena in order to control solidification or glass formation in metals and alloys. Early experiments in nucleation kinetics were accomplished by droplet dispersion methods. Dilatometry was used by Turnbull and others, and more recently differential thermal analysis and differential scanning calorimetry have been used for kinetic studies. These techniques have enjoyed success; however, there are difficulties with these experiments. Since materials are dispersed in a medium, the character of the emulsion/metal interface affects the nucleation behavior. Statistics are derived from the large number of particles observed in a single experiment, but dispersions have a finite size distribution which adds to the uncertainty of the kinetic determinations. Even though temperature can be controlled quite well before the onset of nucleation, the release of the latent heat of fusion during nucleation of particles complicates the assumption of isothermality during these experiments. Containerless processing has enabled another approach to the study of nucleation kinetics. With levitation techniques it is possible to undercool one sample to nucleation repeatedly in a controlled manner, such that the statistics of the nucleation process can be derived from multiple experiments on a single sample. The authors have fully developed the analysis of nucleation experiments on single samples following the suggestions of Skripov. The advantage of these experiments is that the samples are directly observable. The nucleation temperature can be measured by noncontact optical pyrometry, the mass of the sample is known, and post processing analysis can be conducted on the sample. The disadvantages are that temperature measurement must have exceptionally high precision, and it is not possible to isolate specific heterogeneous sites as in droplet dispersions.

Bayuzick, R. J.; Hofmeister, W. H.; Morton, C. M.; Robinson, M. B.

1999-01-01

156

Collision-induced gas phase dissociation rates  

NASA Technical Reports Server (NTRS)

The Landau-Zener theory of reactive cross sections was applied to diatomic molecules dissociating from a ladder of vibrational states. The result predicts a dissociation rate that is quite well duplicated by an Arrhenius function having a preexponential temperature dependence of about T(sub -1/2), at least for inert collision partners. This relation fits experimental data reasonably well. The theory is then used to calculate the effect of vibrational nonequilibrium on dissociation rate. For Morse oscillators, the results are about the same as given by Hammerling, Kivel, and Teare in their analytic approximation for harmonic oscillators, though at very high temperature a correction for the partition function limit is included. The empirical correction for vibration nonequilibrium proposed by Park, which is a convenient algorithm for CFD calculations, is modified to prevent a drastic underestimation of dissociation rates that occurs with this method when vibrational temperature is much smaller than the kinetic temperature of the gas.

Hansen, C. Frederick

1990-01-01

157

Collision-induced gas phase dissociation rates  

NASA Astrophysics Data System (ADS)

The Landau-Zener theory of reactive cross sections was applied to diatomic molecules dissociating from a ladder of vibrational states. The result predicts a dissociation rate that is quite well duplicated by an Arrhenius function having a preexponential temperature dependence of about T(sub -1/2), at least for inert collision partners. This relation fits experimental data reasonably well. The theory is then used to calculate the effect of vibrational nonequilibrium on dissociation rate. For Morse oscillators, the results are about the same as given by Hammerling, Kivel, and Teare in their analytic approximation for harmonic oscillators, though at very high temperature a correction for the partition function limit is included. The empirical correction for vibration nonequilibrium proposed by Park, which is a convenient algorithm for CFD calculations, is modified to prevent a drastic underestimation of dissociation rates that occurs with this method when vibrational temperature is much smaller than the kinetic temperature of the gas.

Hansen, C. Frederick

1990-08-01

158

ATALANTE 2004 Nmes (France) June 21-25, 2004 1 Control of nucleation and crystal growth of a silicate apatitic phase in a glassy matrix  

E-print Network

P39 ATALANTE 2004 Nîmes (France) June 21-25, 2004 1 Control of nucleation and crystal growth@ipgp.jussieu.fr Abstract ­ Nucleation and growth of crystal in an oxide glass was studied in a Si B Al Zr Nd Ca Na O system the crystal nucleation and growth from the parent glass is crucial. In this work, trivalent minor actinides

Paris-Sud XI, Université de

159

Capillary gas chromatography with two new moderately high temperature phases.  

NASA Technical Reports Server (NTRS)

Gas chromatography test results are presented for two new moderately high-temperature phases of Dexsil 400-GC with free hydroxyl end groups (uncapped) and with end groups covered by trimethyl silyl groups (capped). The two Dexsil 400-GC phases were tested for their ability to resolve N-TFA-DL-(+)-2-butyl esters and n-butyl esters, as well as fatty acid methyl esters and hydrocarbon standards. Generally the more polar uncapped phase was superior to the capped phase in all separation comparisons, except for the hydrocarbons.

Pollock, G. E.

1972-01-01

160

Gas Phase Chiral Separations By Ion Mobility Spectrometry  

PubMed Central

This manuscript introduces the concept of Chiral Ion Mobility Spectrometry (CIMS) and presents examples demonstrating the gas phase separation of enantiomers of a wide range of racemates including pharmaceuticals, amino acids and carbohydrates. CIMS is similar to traditional ion mobility spectrometry (IMS), where gas phase ions, when subjected to a potential gradient are separated at atmospheric pressure due to differences in their shapes and sizes. In addition to size and shape, CIMS separates ions based on their stereospecific interaction with a chiral gas. In order to achieve chiral discrimination by CIMS, an asymmetric environment was provided by doping the drift gas with a volatile chiral reagent. In this study S-(+)-2-butanol was used as a chiral modifier to demonstrate enantiomeric separations of atenolol, serine, methionine, threonine, methyl-?-glucopyranoside, glucose, penicillamine, valinol, phenylalanine, and tryptophan from their respective racemic mixtures. PMID:17165808

Dwivedi, Prabha; Wu, Ching; Hill, Herbert H.

2013-01-01

161

Gas-phase observation of multiply charged C60 anions.  

PubMed

Gas-phase observation of C60(1-), C60(3-), and C60(4-) anions generated at platinum and gold electrodes and detected by electrochemical/electrospray mass spectrometry is reported. The anions were electrochemically generated from solutions of C60 dissolved in toluene/acetonitrile as well as from reduction of C60 films on gold electrode surfaces. The gas-phase observation of C60(3-) and C60(4-), despite the fact that they have negative electron affinities, is a result of a Coulombic barrier to electron loss. The fact that C60(2-) was not detected in these experiments is ascribed to its limited solubility under the reaction conditions. These studies, which demonstrate the gas-phase kinetic stability of C60(3-) and C60(4-), illustrate the promise of electrochemical/electrospray mass spectrometry for the study of metastable anions. PMID:16833589

Cammarata, Vince; Guo, Tan; Illies, Andreas; Li, Lidong; Shevlin, Philip

2005-03-31

162

Molecular dynamics of simulation of the nucleation, growth, inhibition and control of gas hydrates. Annual report, March 1992June 1993  

Microsoft Academic Search

This is the second year of a three-year project using molecular simulation techniques tailored specifically for the determination of early-stage kinetics of natural gas hydrate crystal growth and dissolution. This year, extensive simulations of the kinetics of growth of a model system showed the appearance of magic numbers' in the growth rate versus cluster size. The feasibility of monitoring the

1993-01-01

163

Freeze drying for gas chromatography stationary phase deposition  

DOEpatents

The present disclosure relates to methods for deposition of gas chromatography (GC) stationary phases into chromatography columns, for example gas chromatography columns. A chromatographic medium is dissolved or suspended in a solvent to form a composition. The composition may be inserted into a chromatographic column. Alternatively, portions of the chromatographic column may be exposed or filled with the composition. The composition is permitted to solidify, and at least a portion of the solvent is removed by vacuum sublimation.

Sylwester, Alan P. (Livermore, CA)

2007-01-02

164

Gas phase chemical detection with an integrated chemical analysis system  

SciTech Connect

Microfabrication technology has been applied to the development of a miniature, multi-channel gas phase chemical laboratory that provides fast response, small size, and enhanced versatility and chemical discrimination. Each analysis channel includes a sample preconcentrator followed by a gas chromatographic separator and a chemically selective surface acoustic wave detector array to achieve high sensitivity and selectivity. The performance of the components, individually and collectively, is described.

CASALNUOVO,STEPHEN A.; FRYE-MASON,GREGORY CHARLES; KOTTENSTETTE,RICHARD; HELLER,EDWIN J.; MATZKE,CAROLYN M.; LEWIS,PATRICK R.; MANGINELL,RONALD P.; BACA,ALBERT G.; HIETALA,VINCENT M.

2000-04-12

165

Energy partitioning in elementary gas phase reactions  

SciTech Connect

During the last 2{1/2} years we: Measured the LIF excitation spectrum of H atoms dissociated by 193 nm light from cyclopentadiene and indene as well as the rate of dissociation of indene. A general relation is that the translational temperature of the H atoms and the vibrational temperature of the molecules before dissociation are equal. We measured the H atom channel in the photodissociation of ethylene at 193 nm. The LIF excitation spectrum was measured as well as the quantum yield. Isotope effects were observed and explained by RRKM theory in CH{sub 2}CD{sub 2} and trans-CHDCHD. We studied the photodissociation of hydrogen molecules with two photon excited states of the rare gas atoms, 5p(01/2) of Kr and 6p(01/2) of Xe. A new much stronger source of Lyman alpha light at 121.6 nm enabled the study of processes in which a hydride is photodissociated at 121.6 nm and within the same pulse a second photon excites H atom fluorescence. For the first time the dynamics of photodissociation of methane, water, acetylene and HCl were measured at 121.6 nm. Large isotope effects were seen. In CH{sub 3}D, CH{sub 2}D{sub 2} and CD{sub 3}H the H atoms were twice as likely to dissociate as the D atoms.

Bersohn, R.

1991-01-01

166

Stochastic Lindemann kinetics for unimolecular gas-phase reactions.  

PubMed

Lindemann, almost a century ago, proposed a schematic mechanism for unimolecular gas-phase reactions. Here, we present a new semiempirical method to calculate the effective rate constant in unimolecular gas-phase kinetics through a stochastic reformulation of Lindemann kinetics. Considering the rate constants for excitation and de-excitation steps in the Lindemann mechanism as temperature dependent empirical parameters, we construct and solve a chemical master equation for unimolecular gas-phase kinetics. The effective rate constant thus obtained shows excellent agreement with experimental data in the entire concentration range in which it is reported. The extrapolated values of the effective rate constant for very low and very high concentrations of inert gas molecules are in close agreement with values obtained using the Troe semiempirical method. Stochastic Lindemann kinetics, thus, provides a simple method to construct the full falloff curves and can be used as an alternative to the Troe semiempirical method of kinetic data analysis for unimolecular gas-phase reactions. PMID:23879409

Saha, Soma; Dua, Arti

2013-08-22

167

Phase diagrams reveal acid-gas injection subtleties  

SciTech Connect

Examination of phase equilibria in a binary hydrogen sulfide (H{sub 2}S) and water system explains some nuances of acid-gas injection. Also, the phase diagrams dispel some misconceptions, prevalent in literature, on hydrate formation. This article shows how hydrates can form without free water (an aqueous liquid phase) present and how hydrates can also form in the presence of a nonaqueous liquid. This first of a two-part series describes multicomponent phase diagrams. The concluding part will explain acid-gas phase changes from the amine unit to the bottom of an injection well. To replace flaring, acid-gas injection is quickly becoming an environmentally friendly alternative. Acid-gas injection also has attracted the attention of larger producers. With sulfur prices depressed, reinjection could be an economical alternative to building a Claus plant and stockpiling sulfur. It is even possible that injected H{sub 2}S could be produced at a future date if sulfur prices improve.

Carroll, J.J. [Gas Liquids Engineering, Calgary, Alberta (Canada)

1998-03-02

168

Field driven ferromagnetic phase nucleation and propagation from the domain boundaries in antiferromagnetically coupled perpendicular anisotropy films  

SciTech Connect

We investigate the reversal process in antiferromagnetically coupled [Co/Pt]{sub X-1}/{l_brace}Co/Ru/[Co/Pt]{sub X-1}{r_brace}{sub 16} multilayer films by combining magnetometry and Magnetic soft X-ray Transmission Microscopy (MXTM). After out-of-plane demagnetization, a stable one dimensional ferromagnetic (FM) stripe domain phase (tiger-tail phase) for a thick stack sample (X=7 is obtained), while metastable sharp antiferromagnetic (AF) domain walls are observed in the remanent state for a thinner stack sample (X=6). When applying an external magnetic field the sharp domain walls of the thinner stack sample transform at a certain threshold field into the FM stripe domain wall phase. We present magnetic energy calculations that reveal the underlying energetics driving the overall reversal mechanisms.

Hauet, Thomas; Gunther, Christian M.; Hovorka, Ondrej; Berger, Andreas; Im, Mi-Young; Fischer, Peter; Hellwig, Olav

2008-12-09

169

Influence of strain-induced nucleation on the kinetics of phase transformation in a forging steel during warm working  

Microsoft Academic Search

Warm torsion tests were conducted on samples heated to the intercritical (?+?) domain after holding times ranging from 1 to 30 min. A comparison of the kinetics of phase transformation with and without deformation indicated that the acceleration of transformation of ferrite into austenite was related with strain-induced dynamic transformation.

M. A. F Oliveira; A. M Jorge; O Balancin

2004-01-01

170

Solidification: real-time investigation of grain nucleation and growth during liquid to solid phase transformation of aluminum alloys  

Microsoft Academic Search

Aluminum, the most common metallic element in the earth's crust, offers structural materials with high strength and light weight. It is widely used throughout the world economy, particularly in the transportation, packaging, and construction industries. Once extracted from ore, solidification is the most important phase transformation in the development of aluminum products, especially for critical applications. All of these applications

N. Iqbal

2005-01-01

171

Gas phase synthesis and reactivity of dimethylaurate.  

PubMed

A combination of multistage mass spectrometry experiments and DFT calculations were used to examine the synthesis and reactivity of dimethylaurate. Collision induced dissociation (CID) of [(CH(3)CO(2))(4)Au](-) proceeded via reductive elimination of acetylperoxide to yield the diacetate [CH(3)CO(2)AuO(2)CCH(3)](-), which in turn underwent sequential CID decarboxylation reactions to yield the organoaurates [CH(3)CO(2)AuCH(3)](-) and [CH(3)AuCH(3)](-). The unimolecular chemistry of the dimethylaurate proceeds via a combination of bond homolysis to yield the methyl aurate radical anion [CH(3)Au] (-) as well as formation of the gold dihydride [HAuH](-). DFT calculations reveal that the latter anion is formed via a 1,2-dyotropic rearrangement to yield the isomer [CH(3)CH(2)AuH](-), followed by a beta-hydride elimination reaction. Ion-molecule reactions of [CH(3)AuCH(3)](-) with methyl iodide did not yield any products even at relatively high concentrations of the neutral substrate and longer reaction times, indicating a reaction efficiency of less than 1 in 20 000 collisions. DFT calculations were carried out on two different potential energy surfaces (PES) for the reaction of [CH(3)AuCH(3)](-) with CH(3)I: (i) an S(N)2 mechanism proceeding via a side-on transition state; and (ii) a stepwise mechanism proceeding via oxidative addition followed by reductive elimination. Both pathways have significant endothermic barriers, consistent with the lack of C-C bond coupling products being formed in the experiments. Finally, the reactivity of [CH(3)AuCH(3)](-) is compared to the previously studied [CH(3)AgCH(3)](-) and [CH(3)CuCH(3)](-), as well as condensed phase studies on dimethylaurate salts. PMID:20714634

Rijs, Nicole J; Sanvido, Gustavo B; Khairallah, George N; O'Hair, Richard A J

2010-10-01

172

Improvement and further development in CESM/CAM5: gas-phase chemistry and inorganic aerosol treatments  

NASA Astrophysics Data System (ADS)

Gas-phase chemistry and subsequent gas-to-particle conversion processes such as new particle formation, condensation, and thermodynamic partitioning have large impacts on air quality, climate, and public health through influencing the amounts and distributions of gaseous precursors and secondary aerosols. Their roles in global air quality and climate are examined in this work using the Community Earth System Model version 1.0.5 (CESM1.0.5) with the Community Atmosphere Model version 5.1 (CAM5.1) (referred to as CESM1.0.5/CAM5.1). CAM5.1 includes a simple chemistry that is coupled with a 7-mode prognostic Modal Aerosol Model (MAM7). MAM7 includes classical homogenous nucleation (binary and ternary) and activation nucleation (empirical first-order power law) parameterizations, and a highly simplified inorganic aerosol thermodynamics treatment that only simulates particulate-phase sulfate and ammonium. In this work, a new gas-phase chemistry mechanism based on the 2005 Carbon Bond Mechanism for Global Extension (CB05_GE) and several advanced inorganic aerosol treatments for condensation of volatile species, ion-mediated nucleation (IMN), and explicit inorganic aerosol thermodynamics for sulfate, ammonium, nitrate, sodium, and chloride have been incorporated into CESM/CAM5.1-MAM7. Compared to the simple gas-phase chemistry, CB05_GE can predict many more gaseous species, and thus could improve model performance for PM2.5, PM10, PM components, and some PM gaseous precursors such as SO2 and NH3 in several regions as well as aerosol optical depth (AOD) and cloud properties (e.g., cloud fraction (CF), cloud droplet number concentration (CDNC), and shortwave cloud forcing, SWCF) on the global scale. The modified condensation and aqueous-phase chemistry could further improve the prediction of additional variables such as HNO3, NO2, and O3 in some regions, and new particle formation rate (J) and AOD on the global scale. IMN can improve the prediction of secondary PM2.5 components, PM2.5, and PM10 over Europe as well as AOD and CDNC on the global scale. The explicit inorganic aerosol thermodynamics using the ISORROPIA II model improves the prediction of all major PM2.5 components and their gaseous precursors in some regions as well as downwelling shortwave radiation, SWCF, and cloud condensation nuclei at a supersaturation of 0.5% on the global scale. For simulations of 2001-2005 with all the modified and new treatments, the improved model predicts that on global average, SWCF increases by 2.7 W m-2, reducing the normalized mean bias (NMB) of SWCF from -5.4 to 1.2%. Uncertainties in emissions can largely explain the inaccurate prediction of precursor gases (e.g., SO2, NH3, and NO) and primary aerosols (e.g., black carbon and primary organic matter). Additional factors leading to the discrepancies between model predictions and observations include assumptions associated with equilibrium partitioning for fine particles assumed in ISORROPIA II, irreversible gas/particle mass transfer treatment for coarse particles, uncertainties in model treatments such as dust emissions, secondary organic aerosol formation, multi-phase chemistry, cloud microphysics, aerosol-cloud interaction, dry and wet deposition, and model parameters (e.g., accommodation coefficients and prefactors of the nucleation power law) as well as uncertainties in model configuration such as the use of a coarse-grid resolution.

He, J.; Zhang, Y.

2014-09-01

173

Noble metal alloy clusters in the gas phase derived from protein templates: unusual recognition of palladium by gold  

NASA Astrophysics Data System (ADS)

Matrix assisted laser desorption ionization of a mixture of gold and palladium adducts of the protein lysozyme (Lyz) produces naked alloy clusters of the type Au24Pd+ in the gas phase. While a lysozyme-Au adduct forms Au18+, Au25+, Au38+ and Au102+ ions in the gas phase, lysozyme-Pd alone does not form any analogous cluster. Addition of various transition metal ions (Ag+, Pt2+, Pd2+, Cu2+, Fe2+, Ni2+ and Cr3+) in the adducts contributes to drastic changes in the mass spectrum, but only palladium forms alloys in the gas phase. Besides alloy formation, palladium enhances the formation of specific single component clusters such as Au38+. While other metal ions like Cu2+ help forming Au25+ selectively, Fe2+ catalyzes the formation of Au25+ over all other clusters. Gas phase cluster formation occurs from protein adducts where Au is in the 1+ state while Pd is in the 2+ state. The creation of alloys in the gas phase is not affected whether a physical mixture of Au and Pd adducts or a Au and Pd co-adduct is used as the precursor. The formation of Au cores and AuPd alloy cores of the kind comparable to monolayer protected clusters implies that naked clusters themselves may be nucleated in solution.Matrix assisted laser desorption ionization of a mixture of gold and palladium adducts of the protein lysozyme (Lyz) produces naked alloy clusters of the type Au24Pd+ in the gas phase. While a lysozyme-Au adduct forms Au18+, Au25+, Au38+ and Au102+ ions in the gas phase, lysozyme-Pd alone does not form any analogous cluster. Addition of various transition metal ions (Ag+, Pt2+, Pd2+, Cu2+, Fe2+, Ni2+ and Cr3+) in the adducts contributes to drastic changes in the mass spectrum, but only palladium forms alloys in the gas phase. Besides alloy formation, palladium enhances the formation of specific single component clusters such as Au38+. While other metal ions like Cu2+ help forming Au25+ selectively, Fe2+ catalyzes the formation of Au25+ over all other clusters. Gas phase cluster formation occurs from protein adducts where Au is in the 1+ state while Pd is in the 2+ state. The creation of alloys in the gas phase is not affected whether a physical mixture of Au and Pd adducts or a Au and Pd co-adduct is used as the precursor. The formation of Au cores and AuPd alloy cores of the kind comparable to monolayer protected clusters implies that naked clusters themselves may be nucleated in solution. Electronic supplementary information (ESI) available. See DOI: 10.1039/c3nr04257j

Baksi, Ananya; Pradeep, T.

2013-11-01

174

Nucleation and growth of magnetite from solution  

NASA Astrophysics Data System (ADS)

The formation of crystalline materials from solution is usually described by the nucleation and growth theory, where atoms or molecules are assumed to assemble directly from solution. For numerous systems, the formation of the thermodynamically stable crystalline phase is additionally preceded by metastable intermediates . More complex pathways have recently been proposed, such as aggregational processes of nanoparticle precursors or pre-nucleation clusters, which seem to contradict the classical theory. Here we show by cryogenic transmission electron microscopy that the nucleation and growth of magnetite—a magnetic iron oxide with numerous bio- and nanotechnological applications—proceed through rapid agglomeration of nanometric primary particles and that in contrast to the nucleation of other minerals, no intermediate amorphous bulk precursor phase is involved. We also demonstrate that these observations can be described within the framework of classical nucleation theory.

Baumgartner, Jens; Dey, Archan; Bomans, Paul H. H.; Le Coadou, Cécile; Fratzl, Peter; Sommerdijk, Nico A. J. M.; Faivre, Damien

2013-04-01

175

INVESTIGATION OF GAS-PHASE OZONE AS A POTENTIAL BIOCIDE  

EPA Science Inventory

The paper presents data on the effect of ozone on both vegetative and spore-forming fungi as well as on spore-forming bacteria. (NOTE: Despite the wide use of ozone generators in indoor air cleaning, there is little research data on ozone's biocidal activity in the gas phase.) Dr...

176

Oriented xenon hydride molecules in the gas phase  

Microsoft Academic Search

The production of the xenon hydride molecules HXeX with X = I and Cl in the gas phase is reviewed. These molecules are generated by the photolysis of the hydrogen halide HI and HCl molecules on the surface of large xenon Xen clusters. Molecular dynamics simulations show that the flexible H atoms react with the heavy XeX moiety and form

Udo Buck; Michal Fárník

2006-01-01

177

Experiments on gas-phase optically pumped infrared lasers  

Microsoft Academic Search

Population inversions in small gas-phase molecules are produced by optical pumping of vibrational overtone transitions. Efficient frequency down conversion of the pump radiation is obtained by lasing on the inverted transitions. The performance of the lasers is governed by kinetic relaxation and energy exchange processes. The effect of these processes on the ultimate scalability of this class of laser will

Harold C. Miller; Gordon D. Hager

1995-01-01

178

Selected Examples of Gas-Phase Ion Chemistry Studies  

PubMed Central

Gas-phase ion chemistry is an area in mass spectrometry that has received much research interest since the mid fifties of the last century. Although the focus of mass spectrometric research has shifted the last twenty years largely to life science studies, including proteomics, genomics and metabolomics, there are still several groups in the world active in gas-phase ion chemistry of both positive and negative ions, either unimolecularly and/or bimolecularly. In this tutorial lecture the formation and determination of tautomeric ion structures and intra-ionic catalyzed tautomerization in the gas phase will be discussed. In addition, an example of formation of different tautomeric structures in protic and aprotic solvents under electrospray ionization conditions will be given, as established by gas-phase infrared multiphoton dissociation spectroscopy. This will be followed by presenting an example of time-resolved MS/MS which enables to identify the structure of an ion, generated at a particular molecular ion lifetime. At the end of the lecture the power of ion mobility will be shown in elucidating the mechanism of epimerization of bis-Tröger bases having chiral nitrogen centers. PMID:24349921

Nibbering, Nico M. M.

2013-01-01

179

LOW COST IMAGER FOR POLLUTANT GAS LEAK DETECTION - PHASE II  

EPA Science Inventory

An inexpensive imaging Instrument to quickly locate leaks of methane and other greenhouse and VOC gases would reduce the cost and effort expended by industry to comply with EPA regulations. In Phase I, of this WBIR program, a new gas leak visualization camera was demonstrated...

180

Phase separation of a driven granular gas in annular geometry  

Microsoft Academic Search

This work investigates phase separation of a monodisperse gas of inelastically colliding hard disks confined in a two-dimensional annulus, the inner circle of which represents a ``thermal wall.'' When described by granular hydrodynamic equations, the basic steady state of this system is an azimuthally symmetric state of increased particle density at the exterior circle of the annulus. When the inelastic

Manuel Díez-Minguito; Baruch Meerson

2007-01-01

181

Flavin adenine dinucleotide structural motifs: from solution to gas phase.  

PubMed

Flavin adenine dinucleotide (FAD) is involved in important metabolic reactions where the biological function is intrinsically related to changes in conformation. In the present work, FAD conformational changes were studied in solution and in gas phase by measuring the fluorescence decay time and ion-neutral collision cross sections (CCS, in a trapped ion mobility spectrometer, TIMS) as a function of the solvent conditions (i.e., organic content) and gas-phase collisional partner (i.e., N2 doped with organic molecules). Changes in the fluorescence decay suggest that FAD can exist in four conformations in solution, where the abundance of the extended conformations increases with the organic content. TIMS-MS experiments showed that FAD can exist in the gas phase as deprotonated (M = C27H31N9O15P2) and protonated forms (M = C27H33N9O15P2) and that multiple conformations (up to 12) can be observed as a function of the starting solution for the [M + H](+) and [M + Na](+)molecular ions. In addition, changes in the relative abundances of the gas-phase structures were observed from a "stack" to a "close" conformation when organic molecules were introduced in the TIMS cell as collision partners. Candidate structures optimized at the DFT/B3LYP/6-31G(d,p) were proposed for each IMS band, and results showed that the most abundant IMS band corresponds to the most stable candidate structure. Solution and gas-phase experiments suggest that the driving force that stabilizes the different conformations is based on the interaction of the adenine and isoalloxazine rings that can be tailored by the "solvation" effect created with the organic molecules. PMID:25222439

Molano-Arevalo, Juan Camilo; Hernandez, Diana R; Gonzalez, Walter G; Miksovska, Jaroslava; Ridgeway, Mark E; Park, Melvin A; Fernandez-Lima, Francisco

2014-10-21

182

Molecular dynamics of simulation of the nucleation, growth, inhibition and control of gas hydrates. Annual report, March 1992-June 1993  

SciTech Connect

This is the second year of a three-year project using molecular simulation techniques tailored specifically for the determination of early-stage kinetics of natural gas hydrate crystal growth and dissolution. This year, extensive simulations of the kinetics of growth of a model system showed the appearance of magic numbers' in the growth rate versus cluster size. The feasibility of monitoring the kinetics of hydrate growth and dissolution has been demonstrated. A preliminary mechanism for hydrate dissolution has been proposed. A building block' for hydrate growth has been identified as a long-lived entity in the liquid; this single dodecahedron has also been seen by preliminary NMR studies. Inhibition studies have begun with biopolymers and will continue next year with studies of simple inhibitors, in concert with molecular spectroscopic techniques.

Clancy, P.

1993-06-01

183

Measurement and speciation of gas phase peroxides in the atmosphere  

NASA Astrophysics Data System (ADS)

The utility of an improved gas phase sampler and a recently developed nonenzymatic measurement method for H2O2 and HOCH2OOH(HMHP) is demonstrated. The gas phase sampler is equipped with a surfaceless intake to alleviate heterogeneous loss of H2O2 in the sampling line. The nonenzymatic method employs the aqueous phase Fenton reaction for H2O2 measurement and is capable of speciation between H2O2 and HMHP, using a dual channel technique. By adding a third channel employing the well-established method of p-hydroxyphenylacetic acid and horseradish peroxidase for total peroxide measurement, it is possible to differentiate H2O2, HMHP, and other organic peroxides, if present. Preliminary data analysis indicates that the measured total peroxides range from 0.4 to about 6 ppbv, depending on meteorological conditions, and that organic peroxides, mostly HMHP, constitute between 20 and 80 percent of the total peroxides.

Lee, J. H.; Leahy, D. F.; Tang, I. N.; Newman, L.

1993-02-01

184

Liquid-gas phase transition in nuclear matter including strangeness  

SciTech Connect

We apply the chiral SU(3) quark mean field model to study the properties of strange hadronic matter at finite temperature. The liquid-gas phase transition is studied as a function of the strangeness fraction. The pressure of the system cannot remain constant during the phase transition, since there are two independent conserved charges (baryon and strangeness number). In a range of temperatures around 15 MeV (precise values depending on the model used) the equation of state exhibits multiple bifurcates. The difference in the strangeness fraction f{sub s} between the liquid and gas phases is small when they coexist. The critical temperature of strange matter turns out to be a nontrivial function of the strangeness fraction.

Wang, P.; Leinweber, D.B.; Williams, A.G. [Special Research Center for the Subatomic Structure of Matter (CSSM) and Department of Physics, University of Adelaide, Adelaide 5005 (Australia); Thomas, A.W. [Special Research Center for the Subatomic Structure of Matter (CSSM) and Department of Physics, University of Adelaide, Adelaide 5005 (Australia); Jefferson Laboratory, 12000 Jefferson Avenue, Newport News, Virginia 23606 (United States)

2004-11-01

185

Studies of Nucleation and Growth, Specific Heat and Viscosity of Undercooled Melts of Quasicrystals and Polytetrehedral-Phase-Forming Alloys  

NASA Technical Reports Server (NTRS)

By investigating the properties of quasicrystals and quasicrystal-forming liquid alloys, we may determine the role of ordering of the liquid phase in the formation of quasicrystals, leading to a better fundamental understanding of both the quasicrystal and the liquid. A quasicrystal is solid characterized by a symmetric but non-periodic arrangement of atoms, usually in the form of an icosahedron (12 atoms, 20 triangular faces). It is theorized that the short-range order in liquids takes this same form. The degree of ordering depends on the temperature of the liquid, and affects many of the liquid s properties, including specific heat, viscosity, and electrical resistivity. The MSFC role in this project includes solidification studies, phase diagram determination, and thermophysical property measurements on the liquid quasicrystal-forming alloys, all by electrostatic levitation (ESL). The viscosity of liquid quasicrystal-forming alloys is measured by the oscillating drop method, both in the stable and undercooled liquid state. The specific heat of solid, undercooled liquid, and stable liquid are measured by the radiative cooling rate of the droplets.

2003-01-01

186

Communication: Bubbles, crystals, and laser-induced nucleation  

NASA Astrophysics Data System (ADS)

Short intense laser pulses of visible and infrared light can dramatically accelerate crystal nucleation from transparent solutions; previous studies invoke mechanisms that are only applicable for nucleation of ordered phases or high dielectric phases. However, we show that similar laser pulses induce CO2 bubble nucleation in carbonated water. Additionally, in water that is cosupersaturated with argon and glycine, argon bubbles escaping from the water can induce crystal nucleation without a laser. Our findings suggest a possible link between laser-induced nucleation of bubbles and crystals.

Knott, Brandon C.; Larue, Jerry L.; Wodtke, Alec M.; Doherty, Michael F.; Peters, Baron

2011-05-01

187

Gas Phase Chemical Detection with an Integrated Chemical Analysis System  

SciTech Connect

Microfabrication technology has been applied to the development of a miniature, multi-channel gas phase chemical laboratory that provides fast response, small size, and enhanced versatility and chemical discrimination. Each analysis channel includes a sample concentrator followed by a gas chromatographic separator and a chemically selective surface acoustic wave detector array to achieve high sensitivity and selectivity. The performance of the components, individually and collectively, is described. The design and performance of novel micromachined acoustic wave devices, with the potential for improved chemical sensitivity, are also described.

Baca, Albert G.; Casalnuovo, Stephen A.; Frye-Mason, Gregory C.; Heller, Edwin J.; Hietala, Susan L.; Hietala, Vincent M.; Kottenstette, Richard J.; Lewis, Patrick R.; Manginell, Ronald P.; Matzke, Carloyn M.; Reno, John L.; Sasaki, Darryl Y.; Schubert, W. Kent

1999-07-08

188

Nucleation at the contact line observed on nano-textured surfaces  

E-print Network

It has been conjectured that roughness plays a role in surface nucleation, the tendency for freezing to begin preferentially at the liquid-gas interface. Using high speed imaging, we sought evidence for freezing at the contact line on catalyst substrates with imposed characteristic length scales (texture). Length scales consistent with the critical nucleus size and with $\\delta \\sim \\tau / \\sigma$, where $\\tau$ is a relevant line tension and $\\sigma$ is the surface tension, range from nanometers to micron. It is found that nano-scale texture causes a shift in the nucleation of ice in supercooled water to the three-phase contact line, while micro-scale texture does not.

Gurganus, C W; Kostinski, A B; Shaw, R A

2014-01-01

189

Collaborative Advanced Gas Turbine Program: Phase 1. Final report  

SciTech Connect

The Collaborative Advanced Gas Turbine (CAGT) Program is an advanced gas turbine research and development program whose goal is to accelerate the commercial availability, to within the turn of the century, of high efficiency aeroderivative gas turbines for electric power generating applications. In the first project phase, research was conducted to prove or disprove the research hypothesis that advanced aeroderivative gas turbine systems can provide a promising technology alternative, offering high efficiency and good environmental performance characteristics in modular sizes, for utility applications. This $5 million, Phase 1 research effort reflects the collaborative efforts of a broad and international coalition of industries and organizations, both public and private, that have pooled their resources to assist in this research. Included in this coalition are: electric and gas utilities, the Electric Power Research Institute, the Gas Research Institute and the principal aircraft engine manufacturers. Additionally, the US Department of Energy (DOE) and the California Energy Commission have interacted with the CAGT on both technical and executive levels as observers and sources of funding. The three aircraft engine manufacturer-led research teams participating in this research include: Rolls-Royce, Inc., and Bechtel; the Turbo Power and Marine Division of United Technologies and Fluor Daniel; and General Electric Power Generation, Stewart and Stevenson, and Bechtel. Each team has investigated advanced electric power generating systems based on their high-thrust (60,000 to 100,000 pounds) aircraft engines. The ultimate goal of the CAGT program is that the community of stakeholders in the growing market for natural-gas-fueled, electric power generation can collectively provide the right combination of market-pull and technology-push to substantially accelerate the commercialization of advanced, high efficiency aeroderivative technologies.

Hollenbacher, R.; Kesser, K.; Beishon, D.

1994-12-01

190

The organic matter of Comet Halley as inferred by joint gas phase and solid phase analyses  

NASA Astrophysics Data System (ADS)

During encounters with Comet Halley, the experiment PICCA onboard Giotto measured the gas-phase organic ion composition of the coma, and the experiment PUMA onboard Vega-1 measured the dust composition. Joining both results gives a consistent picture of the parent organic matter from which dust and gas is produced: a complex unsaturated polycondensate, which splits during coma formation into the more refractory C=C,C-N-containing dust part and the more volatile C=C,C-O-containing gas part. The responsible exothermal chemical reactions, which are triggered by sunlight, may play a major role in the dynamics of coma formation.

Krueger, F. R.; Korth, A.; Kissel, J.

1991-04-01

191

Gas-Phase Synthesis of Gold- and Silica-Coated Nanoparticles  

NASA Astrophysics Data System (ADS)

Composite nanoparticles consisting of separate core-shell materials are of interest for a variety of biomedical and industrial applications. By combining different materials at the nanoscale, particles can exhibit enhanced or multi-functional behavior such as plasmon resonance combined with superparamagnetism. Gas-phase nanoparticle synthesis processes are promising because they can continuously produce particles with high mass-yield rates. In this dissertation, new methods are investigated for producing gas-phase coatings of nanoparticles in an "assembly-line" fashion. Separate processes are developed to create coatings from silica and gold that can be used with a variety of core-particle chemistries. A photoinduced chemical vapor deposition (photo-CVD) method is used to produce silica coatings from tetraethyl orthosilicate (TEOS) on the surface of nanoparticles (diameter ˜5--70 nm). Tandem differential mobility analysis (TDMA) of the process demonstrates that particle coatings can be produced with controllable thicknesses (˜1--10 nm) by varying system parameters such as precursor flow rate. Electron microscopy and infrared spectroscopy confirm that the photo-CVD films uniformly coat the particles and that the coatings are silica. In order to describe the coating process a chemical mechanism is proposed that includes gas-phase, surface and photochemical reactions. A chemical kinetics model of the mechanism indicates that photo-CVD coating proceeds primarily through the photodecomposition of TEOS which removes ethyl groups, thus creating activated TEOS species. The activated TEOS then adsorbs onto the surface of the particle where a series of subsequent reactions remove the remaining ethyl groups to produce a silica film with an open site for further attachment. The model results show good agreement with the experimentally measured coating trends, where increased TEOS flow increases coating thickness and increased nitrogen flow decreases coating thickness. Gold decoration of nanoparticles is accomplished by evaporation of solid gold in the presence of an aerosol flow. A hot-wire generation method is developed where gold particles are produced from a composite gold-platinum wire. Investigations of the hot-wire generator show that it can produce particles with a range of sizes and that more uniform, non-agglomerated particles are produced when using smaller diameter tubes where gas velocities across the wire are higher and recirculation zones are diminished. When gold is evaporated in the presence of silica nanoparticles, the silica aerosol is decorated by gold through either homogeneous gold nucleation and subsequent scavenging by the silica nanoparticles, or by heterogeneous nucleation on the silica surface in which the gold "balls up" due to the high surface tension of gold on silica. In both cases the resulting particles exhibit a plasmon absorbance resonance typical of gold nanoparticles (lambda˜550 nm). Finally, the silica coating and gold decoration processes are combined with a thermal plasma technique for synthesizing iron-oxide to produce tri-layer nanoparticles.

Boies, Adam Meyer

192

Spectroscopic studies of cold, gas-phase biomolecular ions  

NASA Astrophysics Data System (ADS)

While the marriage of mass spectrometry and laser spectroscopy is not new, developments over the last few years in this relationship have opened up new horizons for the spectroscopic study of biological molecules. The combination of electrospray ionisation for producing large biological molecules in the gas phase together with cooled ion traps and multiple-resonance laser schemes are allowing spectroscopic investigation of individual conformations of peptides with more than a dozen amino acids. Highly resolved infrared spectra of single conformations of such species provide important benchmarks for testing the accuracy of theoretical calculations. This review presents a number of techniques employed in our laboratory and in others for measuring the spectroscopy of cold, gas-phase protonated peptides. We show examples that demonstrate the power of these techniques and evaluate their extension to still larger biological molecules.

Rizzo, Thomas R.; Stearns, Jaime A.; Boyarkin, Oleg V.

193

Superfluidity and phase transitions in a resonant Bose gas  

SciTech Connect

The atomic Bose gas is studied across a Feshbach resonance, mapping out its phase diagram, and computing its thermodynamics and excitation spectra. It is shown that such a degenerate gas admits two distinct atomic and molecular superfluid phases, with the latter distinguished by the absence of atomic off-diagonal long-range order, gapped atomic excitations, and deconfined atomic {pi}-vortices. The properties of the molecular superfluid are explored, and it is shown that across a Feshbach resonance it undergoes a quantum Ising transition to the atomic superfluid, where both atoms and molecules are condensed. In addition to its distinct thermodynamic signatures and deconfined half-vortices, in a trap a molecular superfluid should be identifiable by the absence of an atomic condensate peak and the presence of a molecular one.

Radzihovsky, Leo [Department of Physics, University of Colorado, Boulder, CO 80309 (United States); Weichman, Peter B. [BAE Systems, Advanced Information Technologies, 6 New England Executive Park, Burlington, MA 01803 (United States); Park, Jae I. [Department of Physics, University of Colorado, Boulder, CO 80309 (United States); National Institute of Standards and Technology, 325 Broadway, Boulder, CO 80305-3328 (United States)], E-mail: jae@nist.gov

2008-10-15

194

FORMATION OF POLYCYCLIC AROMATIC HYDROCARBONS AND CARBONACEOUS SOLIDS IN GAS-PHASE CONDENSATION EXPERIMENTS  

SciTech Connect

Carbonaceous grains represent a major component of cosmic dust. In order to understand their formation pathways, they have been prepared in the laboratory by gas-phase condensation reactions such as laser pyrolysis and laser ablation. Our studies demonstrate that the temperature in the condensation zone determines the formation pathway of carbonaceous particles. At temperatures lower than 1700 K, the condensation by-products are mainly polycyclic aromatic hydrocarbons (PAHs) that are also the precursors or building blocks for the condensing soot grains. The low-temperature condensates contain PAH mixtures that are mainly composed of volatile three to five ring systems. At condensation temperatures higher than 3500 K, fullerene-like carbon grains and fullerene compounds are formed. Fullerene fragments or complete fullerenes equip the nucleating particles. Fullerenes can be identified as soluble components. Consequently, condensation products in cool and hot astrophysical environments such as cool and hot asymptotic giant branch stars or Wolf-Rayet stars should be different and should have distinct spectral properties.

Jaeger, C.; Huisken, F.; Henning, Th. [Max-Planck-Institut fuer Astronomie, Koenigstuhl 17, D-69117 Heidelberg (Germany); Mutschke, H.; Jansa, I. Llamas [Astrophysikalisches Institut und Universitaets-Sternwarte (AIU), Friedrich-Schiller-Universitaet Jena, Schillergaesschen 2-3, D-07745 Jena (Germany)], E-mail: Cornelia.Jaeger@uni-jena.de

2009-05-01

195

Impact of nuclear irradiation on helium bubble nucleation at interfaces in liquid metals coupled to permeation through stainless steels  

E-print Network

The impact of nucleating gas bubbles in the form of a dispersed gas phase on hydrogen isotope permeation at interfaces between liquid metals, like LLE, and structural materials, like stainless steel, has been studied. Liquid metal to structural material interfaces involving surfaces, may lower the nucleation barrier promoting bubble nucleation at active sites. Hence, hydrogen isotope absorption into gas bubbles modelling and control at interfaces may have a capital importance regarding design, operation and safety. He bubbles as a permeation barrier principle is analysed showing a significant impact on hydrogen isotope permeation, which may have a significant effect on liquid metal systems, e.g., tritium extraction systems. Liquid metals like LLE under nuclear irradiation in, e.g., breeding blankets of a nuclear fusion reactor would generate tritium which is to be extracted and recirculated as fuel. At the same time that tritium is bred, helium is also generated and may precipitate in the form of nano bubbles...

Fradera, Jorge

2013-01-01

196

Molecular Tagging Velocimetry (MTV) measurements in gas phase flows  

NASA Astrophysics Data System (ADS)

Recent developments in Molecular Tagging Velocimetry (MTV) using the phosphorescence of biacetyl are described for gas-phase flows. With improvements in tagging, detection, and processing schemes, whole-field measurements of two components of the velocity vector are obtained simultaneously, typically at more than 300 points over a plane. Application of this measurement approach is demonstrated in mapping the velocity and vorticity fields of the intake flow into a ``steady flow rig'' model of an internal combustion engine.

Stier, B.; Koochesfahani, M. M.

197

A multiwatt all gas-phase iodine laser (AGIL)  

Microsoft Academic Search

The demonstration and characterization of a multiwatt All Gas-phase Iodine Laser (AGIL) are described. A 20-cm subsonic reactor was used to produce NCl(a1Delta) for a series parametric studies of the I*(2P1\\/2) - I(2P3\\/2) small signal gain and extracted power dependence on reactant flow rates and reaction time. A reduction in the flow channel height led to improved performance. The highest

Gerald C. Manke II; Chris B. Cooper; Shiv C. Dass; Timothy J. Madden; Gordon D. Hager

2004-01-01

198

Gas phase photocatalytic removal of toluene effluents on sulfated titania  

Microsoft Academic Search

Photocatalytic removal of toluene in the gas phase was carried out over UV-illuminated sulfated titania materials in a cylinder-like continuous reactor. A series of SO42?–TiO2 samples was obtained from the addition of H2SO4 on an amorphous titanium hydroxide gel synthesized according to a classical sol–gel procedure. The wide variety of materials led to varying photocatalytic behaviors depending strongly on the

Elodie Barraud; Florence Bosc; David Edwards; Nicolas Keller; Valérie Keller

2005-01-01

199

Molecular Tagging Velocimetry (MTV) measurements in gas phase flows  

Microsoft Academic Search

Recent developments in Molecular Tagging Velocimetry (MTV) using the phosphorescence of biacetyl are described for gas-phase flows. With improvements in tagging, detection, and processing\\u000a schemes, whole-field measurements of two components of the velocity vector are obtained simultaneously, typically at more\\u000a than 300 points over a plane. Application of this measurement approach is demonstrated in mapping the velocity and vorticity\\u000a fields

B. Stier; M. M. Koochesfahani

1999-01-01

200

Entropy effects in gas phase ion-molecule association reactions  

Microsoft Academic Search

The kinetics of gas phase reactions of the ions C5H5M+ (M=V, Co, Ni and Ru) with oxygen (Me2CO, Me2O, MeOH, Me2CHOH, H2O) and nitrogen (NH3, NH2Me, NHMe2, NMe3) donor ligands have been studied by Ion Trap Mass Spectrometry. The kinetic data confirm the previously found dependence of the log of the rate constants upon the ligand ionization energy. To get

Sandro Torroni; Andrea Maranzana

2001-01-01

201

Novel five-membered ring intermediates in gas phase reactions  

Microsoft Academic Search

This review considers the role of closed-ring intermediates in chemistry, in general, and focuses on recent experimental and\\u000a theoretical works that provide compelling evidence for a fivemembered ring intermediate in the gas phase. The reactions of\\u000a oxygen atoms with ethyl iodide and larger alkyl iodides produce HOI and a corresponding ethylenic compound via attack of the\\u000a oxygen atom at the

Richard A. Loomis; Stephen R. Leone; Mary K. Gilles

1998-01-01

202

Breakdown of a topological phase: Quantum phase transition in a loop gas model with tension  

Microsoft Academic Search

We discuss the stability of topological order against local perturbations by considering the effect of a magnetic field on a spin model -- the toric code -- which is in a topological phase. The model can be mapped onto a quantum loop gas where the perturbation introduces a bare loop tension. When the loop tension is small, the topological order

Simon Trebst; Philipp Werner; Matthias Troyer; Kirill Shtengel; Chetan Nayak

2007-01-01

203

BreakdownofaTopological Phase:QuantumPhaseTransitioninaLoopGasModel withTension  

Microsoft Academic Search

We study the stability of topological order against local perturbations by considering the effect of a magnetic field on a spin model—the toric code —which is in a topological phase. The model can be mapped onto a quantum loop gas where the perturbation introduces a bare loop tension. When the loop tension is small, the topological order survives. When it

Simon Trebst; Philipp Werner; Matthias Troyer; Kirill Shtengel; Chetan Nayak

2007-01-01

204

GAS PHASE SELECTIVE PHOTOXIDATION OF ALCOHOLS USING LIGHT-ACTIVATED TITANIUM DIOXIDE AND MOLECULAR OXYGEN  

EPA Science Inventory

Gas Phase Selective Oxidation of Alcohols Using Light-Activated Titanium Dioxide and Molecular Oxygen Gas phase selective oxidations of various primary and secondary alcohols are studied in an indigenously built stainless steel up-flow photochemical reactor using ultravi...

205

Revision of the thermodynamics of the proton in gas phase.  

PubMed

Proton transfer is ubiquitous in various physical/chemical processes, and the accurate determination of the thermodynamic parameters of the proton in the gas phase is useful for understanding and describing such reactions. However, the thermodynamic parameters of such a proton are usually determined by assuming the proton as a classical particle whatever the temperature. The reason for such an assumption is that the entropy of the quantum proton is not always soluble analytically at all temperatures. Thereby, we addressed this matter using a robust and reliable self-consistent iterative procedure based on the Fermi-Dirac formalism. As a result, the free proton gas can be assumed to be classical for temperatures higher than 200 K. However, it is worth mentioning that quantum effects on the gas phase proton motion are really significant at low temperatures (T ? 120 K). Although the proton behaves as a classical particle at high temperatures, we strongly recommend the use of quantum results at all temperatures, for the integrated heat capacity and the Gibbs free energy change. Therefore, on the basis of the thermochemical convention that ignores the proton spin, we recommend the following revised values for the integrated heat capacity and the Gibbs free energy change of the proton in gas phase and, at the standard pressure (1 bar): ?H0?T = 6.1398 kJ mol(-1) and ?G0?T = -26.3424 kJ mol(-1). Finally, it is important noting that the little change of the pressure from 1 bar to 1 atm affects notably the entropy and the Gibbs free energy change of the proton. PMID:25338234

Fifen, Jean Jules; Dhaouadi, Zoubeida; Nsangou, Mama

2014-11-20

206

Nucleation on active centers in confined volumes.  

PubMed

Kinetic equations describing nucleation on active centers are solved numerically to determine the number of supercritical nuclei, nucleation rate, and the number density of nuclei for formation both of droplets from vapor and also crystalline phase from vapor, solution, and melt. Our approach follows standard nucleation model, when the exhaustion of active centers is taken into account via the boundary condition, and thus no additional equation (expressing exhaustion of active centers) is needed. Moreover, we have included into our model lowering of supersaturation of a mother phase as a consequence of the phase transition process within a confined volume. It is shown that the standard model of nucleation on active centers (Avrami approach) gives faster exhaustion of active centers as compared with our model in all systems under consideration. Nucleation rate (in difference to standard approach based on Avrami model) is equal to the time derivative of the total number of nuclei and reaches some maximum with time. At lower nucleation barrier (corresponding to higher initial supersaturation or lower wetting angle of nucleus on the surface of active center) the exhaustion of active centers is faster. Decrease in supersaturation of the mother phase is faster at higher number of active centers. PMID:22559495

Kožíšek, Zden?k; Hikosaka, Masamichi; Okada, Kiyoka; Demo, Pavel

2012-04-28

207

Ice-Nucleating Bacteria  

NASA Astrophysics Data System (ADS)

Since the discovery of ice-nucleating bacteria in 1974 by Maki et al., a large number of studies on the biological characteristics, ice-nucleating substance, ice nucleation gene and frost damage etc. of the bacteria have been carried out. Ice-nucleating bacteria can cause the freezing of water at relatively warm temperature (-2.3°C). Tween 20 was good substrates for ice-nucleating activity of Pseudomonas fluorescens KUIN-1. Major fatty acids of Isolate (Pseudomonas fluorescens) W-11 grown at 30°C were palmitic, cis-9-hexadecenoic and cis-11-octadecenoic which amounted to 90% of the total fatty acids. Sequence analysis shows that an ice nucleation gene from Pseudomonas fluorescens is related to the gene of Pseudomonas syringae.

Obata, Hitoshi

208

Nucleation-induced transition to collective motion in active systems  

NASA Astrophysics Data System (ADS)

While the existence of polar ordered states in active systems is well established, the dynamics of the self-assembly processes are still elusive. We study a lattice gas model of self-propelled elongated particles interacting through excluded volume and alignment interactions, which shows a phase transition from an isotropic to a polar ordered state. By analyzing the ordering process we find that the transition is driven by the formation of a critical nucleation cluster and a subsequent coarsening process. Moreover, the time to establish a polar ordered state shows a power-law divergence.

Weber, Christoph A.; Schaller, Volker; Bausch, Andreas R.; Frey, Erwin

2012-09-01

209

Gas phase oxidation downstream of a catalytic combustor  

NASA Technical Reports Server (NTRS)

Effect of the length available for gas-phase reactions downstream of the catalytic reactor on the emission of CO and unburned hydrocarbons was investigated. A premixed, prevaporized propane/air feed to a 12/cm/diameter catalytic/reactor test section was used. The catalytic reactor was made of four 2.5 cm long monolithic catalyst elements. Four water cooled gas sampling probes were located at positions between 0 and 22 cm downstream of the catalytic reactor. Measurements of unburned hydrocarbon, CO, and CO2 were made. Tests were performed with an inlet air temperature of 800 K, a reference velocity of 10 m/s, pressures of 3 and 600,000 Pa, and fuel air equivalence ratios of 0.14 to 0.24. For very lean mixtures, hydrocarbon emissions were high and CO continued to be formed downstream of the catalytic reactor. At the highest equivalence ratios tested, hydrocarbon levels were much lower and CO was oxidized to CO2 in the gas phase downstream. To achieve acceptable emissions, a downstream region several times longer than the catalytic reactor could be required.

Tien, J. S.; Anderson, D. N.

1979-01-01

210

Specific, trace gas induced phase transition in copper(II)oxide for highly selective gas sensing  

NASA Astrophysics Data System (ADS)

Here, we present results on the investigation of the percolation phase transition in copper(II)oxide (CuO) and show how it may be used to determine trace gas concentrations. This approach provides a highly selective sensing mechanism for the detection of hydrogen sulfide even in oxygen depleted atmospheres. In real-world applications, this scenario is encountered in biogas plants and natural gas facilities, where reliable H2S sensing and filtering are important because of the destructive effects H2S has on machinery. As opposed to gas detection via standard metal-oxide reaction routes, the percolation dynamics are demonstrated to be independent of the surface morphology in accordance with the universality of phase transitions. The sensing behavior of ink-jet printed CuO layers was tested for a large set of parameters including layer temperature, hydrogen sulfide (H2S) and oxygen concentration, as well as the sensitivity towards other gas species. The electrical percolation of the sensing layer is heralded by a dramatic drop in the overall resistivity of the CuO layer for temperatures below 200 °C. The observed percolation phenomena in this temperature regime are unique to H2S even in comparison with related volatile thio-compounds making the sensing mechanism highly selective. At elevated temperatures above 300 °C, the phase transition does not occur. This enables two distinct operational modes which are tunable via the sensor temperature and also allows for resetting the sensing layer after an electrical breakthrough.

Kneer, J.; Wöllenstein, J.; Palzer, S.

2014-08-01

211

Measurement and speciation of gas phase peroxides in the atmosphere  

SciTech Connect

An improved gas phase sampler and a recently developed nonenzymatic measurement method for H[sub 2]O[sub 2] and HOCH[sub 2]OOH(HMHP) are described. The gas phase sampler is equipped with a surfaceless intake to alleviate heterogeneous loss of H[sub 2]O[sub 2] in the sampling line. The nonenzymatic method makes use of the aqueous phase Fention reaction for H[sub 2]O[sub 2] measurement and is capable of speciation between H[sub 2]O[sub 2] and HMHP, using a dual channel technique. By adding a third channel employing the well-established method of p-hydroxyphenylacetic acid (POHPAA) and horseradish peroxidase for total peroxide measurement, it is possible to differentiate H[sub 2]O[sub 2], HMHP, and other organic peroxides, if present. The measurement technique was successfully deployed in a field study at George L. Smith III State Park, Georgia (82[degrees]20[prime]W, 32[degrees]30[prime]N). Preliminary data analysis indicates that the measured total peroxides range from 0.4 to [approximately]6 ppbv, depending on meteorological conditions, and that organic peroxides, mostly HMHP, constitute between 20 and 80% of the total peroxides. The work reported here represents the first continuous and real-time measurements for these peroxides in the atmosphere. 28 refs., 7 figs., 1 tab.

Lee, J.H.; Leahy, D.F.; Tang, I.N.; Newman, L. (Brookhaven National Lab., Upton, NY (United States))

1993-02-20

212

Gas phase contributions to topochemical hydride reduction reactions  

SciTech Connect

Alkali and alkali earth hydrides have been used as solid state reductants recently to yield many interesting new oxygen-deficient transition metal oxides. These reactions have tacitly been assumed to be a solid phase reaction between the reductant and parent oxide. We have conducted a number of experiments with physical separation between the reductant and oxides, and find that in some cases reduction proceeds even when the reagents are physically separated, implying reactions with in-situ generated H{sub 2} and, to a lesser extent, getter mechanisms. Our findings change our understanding of these topochemical reactions, and should enhance the synthesis of additional new oxides and nanostructures. - Graphical abstract: Topochemical reductions with hydrides: Solid state or gas phase reaction? Display Omitted - Highlights: • SrFeO{sub 2} and LaNiO{sub 2} were prepared by topochemical reduction of oxides. • Separating the reducing agent (CaH{sub 2}, Mg metal) from the oxide still results in reduction. • Such topochemical reactions can occur in the gas phase.

Kobayashi, Yoji [Department of Energy and Hydrocarbon Chemistry, Graduate School of Engineering, Kyoto University, Nishikyo-ku, Kyoto 615-8510 (Japan); CREST, Japan Science and Technology Agency (JST), Kawaguchi, Saitama 332-0012 (Japan); Li, Zhaofei [Institute for Integrated Cell-Material Sciences, Kyoto University, Sakyo-ku, Kyoto 606-8502 (Japan); Hirai, Kei [Institute for Chemical Research, Kyoto University, Gokasho, Uji, Kyoto 611-0011 (Japan); Tassel, Cédric [Department of Energy and Hydrocarbon Chemistry, Graduate School of Engineering, Kyoto University, Nishikyo-ku, Kyoto 615-8510 (Japan); The Hakubi Center for Advanced Research, Kyoto University, Yoshida-Ushinomiya-cho, Sakyo-ku, Kyoto 606-8302 (Japan); Loyer, François [Department of Energy and Hydrocarbon Chemistry, Graduate School of Engineering, Kyoto University, Nishikyo-ku, Kyoto 615-8510 (Japan); Institut des Sciences Chimiques de Rennes, UMR 6226 Université de Rennes 1-CNRS, équipe CSM, Bât. 10B, Campus de Beaulieu, 263, Avenue du Général Leclerc, 35042 Rennes Cedex (France); Ichikawa, Noriya [CREST, Japan Science and Technology Agency (JST), Kawaguchi, Saitama 332-0012 (Japan); Institute for Chemical Research, Kyoto University, Gokasho, Uji, Kyoto 611-0011 (Japan); Abe, Naoyuki [Department of Energy and Hydrocarbon Chemistry, Graduate School of Engineering, Kyoto University, Nishikyo-ku, Kyoto 615-8510 (Japan); Department of Chemistry, Graduate School of Science, Kyoto University, Sakyo-ku, Kyoto 606-8502 (Japan); Yamamoto, Takafumi [Department of Energy and Hydrocarbon Chemistry, Graduate School of Engineering, Kyoto University, Nishikyo-ku, Kyoto 615-8510 (Japan); Shimakawa, Yuichi [CREST, Japan Science and Technology Agency (JST), Kawaguchi, Saitama 332-0012 (Japan); Institute for Chemical Research, Kyoto University, Gokasho, Uji, Kyoto 611-0011 (Japan); and others

2013-11-15

213

Experiments on Nucleation in Different Flow Regimes  

NASA Technical Reports Server (NTRS)

The vast majority of metallic engineering materials are solidified from the liquid phase. Understanding the solidification process is essential to control microstructure, which in turn, determines the properties of materials. The genesis of solidification is nucleation, where the first stable solid forms from the liquid phase. Nucleation kinetics determine the degree of undercooling and phase selection. As such, it is important to understand nucleation phenomena in order to control solidification or glass formation in metals and alloys. Early experiments in nucleation kinetics were accomplished by droplet dispersion methods [1-6]. Dilitometry was used by Turnbull and others, and more recently differential thermal analysis and differential scanning calorimetry have been used for kinetic studies. These techniques have enjoyed success; however, there are difficulties with these experiments. Since materials are dispersed in a medium, the character of the emulsion/metal interface affects the nucleation behavior. Statistics are derived from the large number of particles observed in a single experiment, but dispersions have a finite size distribution which adds to the uncertainty of the kinetic determinations. Even though temperature can be controlled quite well before the onset of nucleation, the release of the latent heat of fusion during nucleation of particles complicates the assumption of isothermality during these experiments. Containerless processing has enabled another approach to the study of nucleation kinetics [7]. With levitation techniques it is possible to undercool one sample to nucleation repeatedly in a controlled manner, such that the statistics of the nucleation process can be derived from multiple experiments on a single sample. The authors have fully developed the analysis of nucleation experiments on single samples following the suggestions of Skripov [8]. The advantage of these experiments is that the samples are directly observable. The nucleation temperature can be measured by noncontact optical pyrometry, the mass of the sample is known, and post processing analysis can be conducted on the sample. The disadvantages are that temperature measurement must have exceptionally high precision, and it is not possible to isolate specific heterogeneous sites as in droplet dispersions.

Bayuzick, Robert J.

1999-01-01

214

Mechanisms of the water-gas-shift reaction by iron pentacarbonyl in the gas phase.  

PubMed

We analyzed the mechanisms of the water-gas-shift reaction catalyzed by Fe(CO) 5/OH (-) in the gas phase using DFT methods. The systematic analysis of the accessible reaction mechanisms and the consideration of the Gibbs free energies allows for different reaction routes than previously suggested. In the dominant catalytic cycle, the hydride [FeH(CO) 4]- is the important intermediate. Associative reaction mechanisms are not favorable under moderate and low pressures. At high pressure, a side reaction takes over and prevents the conversion of H 2O and CO to H 2 and CO 2 and leads to the formation of HCOOH. PMID:18754658

Rozanska, Xavier; Vuilleumier, Rodolphe

2008-10-01

215

Lattice-Gas Simulations of Minority-Phase Domain Growth in Binary Immiscible and Ternary Amphiphilic Fluid  

E-print Network

We investigate the growth kinetics of binary immiscible fluids and emulsions in two dimensions using a hydrodynamic lattice-gas model. We perform off-critical quenches in the binary fluid case and find that the domain size within the minority phase grows algebraically with time in accordance with theoretical predictions. In the late time regime we find a growth exponent n = 0.45 over a wide range of concentrations, in good agreement with other simluations. In the early time regime we find no universal growth exponent but a strong dependence on the concentration of the minority phase. In the ternary amphiphilic fluid case the kinetics of self assembly of the droplet phase are studied for the first time. At low surfactant concentrations, we find that, after an early algebraic growth, a nucleation regime dominates the late-time kinetics, which is enhanced by an increasing concentration of surfactant. With a further increase in the concentration of surfactant, we see a crossover to logarithmically slow growth, and finally saturation of the oil droplets, which we fit phenomenologically to a stretched exponential function. Finally, the transition between the droplet and the sponge phase is studied.

Florian W. J. Weig; Peter V. Coveney; Bruce M. Boghosian

1997-05-24

216

SIMULATION OF AEROSOL FORMATION IN GAS-LIQUID CONTACT DEVICES  

Microsoft Academic Search

In gas-liquid contact devices like absorbers, quench coolers, or condensers, aerosols can be formed by spontaneous phase transitions, initiated by homogeneous or heterogeneous nucleation, if a supersaturated gas phase emerges due to simultaneous heat and mass transfer processes or chemical reactions. Typical examples are the absorption of acid gases, like HCl or SO3, the condensation of solvents in the presence

A. Wix; K. Schaber; O. Ofenloch; R. Ehrig; P. Deuflhard

2007-01-01

217

Gas-phase silicon micromachining with xenon difluoride  

NASA Astrophysics Data System (ADS)

Xenon difluoride is a gas phase, room temperature, isotropic silicon etchant with extremely high selectivity to many materials commonly used in microelectromechancial systems, including photoresists, aluminum, and silicon dioxide. Using a simple vacuum system, the effects of etch aperture and loading were explored for etches between 10 and 200 micrometers . Etch rates as high as 40 micrometers /minute were observed. Initial characteriation of wafer surface temperature during the etch indicates tens of degrees of self-heating, which is known to cause substantial decrease in etch rate.

Chang, Floy I.; Yeh, Richard; Lin, Gisela; Chu, Patrick B.; Hoffman, Eric G.; Kruglick, Ezekiel J.; Pister, Kristofer S. J.; Hecht, Michael H.

1995-09-01

218

Mulitwatt all gas-phase iodine laser (AGIL)  

Microsoft Academic Search

The demonstration and characterization of a multi-watt All Gas-phase Iodine Laser (AGIL) are described. A 20-cm subsonic reactor was used to produce NCl(a1Delta) for a series of parametric studies of the I*(2P1\\/2)-I(2P3\\/2) small signal gain and extracted power dependence on reactant flow rates and reaction time. The highest measured gain was 2.5x10-4 cm-1 and the highest power observed was 18

Gerald C. Manke II; Chris B. Cooper; Shiv C. Dass; Timothy J. Madden; Gordon D. Hager

2003-01-01

219

The solar system/interstellar medium connection - Gas phase abundances  

NASA Technical Reports Server (NTRS)

Gas-phase abundances in the outer solar system are presented as diagnostics of the interstellar medium at the time of the solar system formation, some 4.55 billion years ago. Possible influences of the thermal and chemical histories of the primitive solar nebula and of the processes which led to the formation and evolution of the outer planets and comets on the elemental and molecular composition of the primordial matter are outlined. The major components of the atmospheres of the outer planets and of the comae of comets are identified, and the cosmogonical and cosmological implications are discussed.

Lutz, Barry L.

1987-01-01

220

The gas phase reactions of methylene with propionaldehyde  

E-print Network

carbonyls (30) was reported by Back . In this work acetaldehyde, propionaldehyde and formaldehyde were reacted in the gas phase with methylene. The main products found in the reaction with acetaldehyde were carbon monoxide, methane, ethane, ethylene... on the basis of oxygen effects on the 1, Z-epoxybutane yield. A singlet biradical like (I) is expected to close to 1, 2-epoxybutane rapidly, and a radical scavanger such as oxygen would not react with a singlet biradical such as ( I) rapidly enough to trap...

Fuqua, Peter Joseph

2012-06-07

221

Gas-phase energetics of thorium fluorides and their ions.  

PubMed

Gas-phase thermochemistry for neutral ThF(n) and cations ThF(n)(+) (n = 1-4) is obtained from large-basis CCSD(T) calculations, with a small-core pseudopotential on thorium. Electronic partition functions are computed with the help of relativistic MRCI calculations. Geometries, vibrational spectra, electronic fine structure, and ion appearance energies are tabulated. These results support the experimental results by Lau, Brittain, and Hildenbrand for the neutral species, except for ThF. The ion thermochemistry is presented here for the first time. PMID:23137388

Irikura, Karl K

2013-02-14

222

Neurotransmitters in the Gas Phase: La-Mb Studies  

NASA Astrophysics Data System (ADS)

LA-MB-FTMW spectroscopy combines laser ablation with Fourier transform microwave spectroscopy in supersonic jets overcoming the problems of thermal decomposition associated with conventional heating methods. We present here the results on LA-MB-FTMW studies of some neurotransmitters. Six conformers of dopamine, four of adrenaline, five of noradrenaline and three conformers of serotonin have been characterized in the gas phase. The rotational and nuclear quadrupole coupling constants extracted from the analysis of the rotational spectrum are directly compared with those predicted by ab initio methods to achieve the conclusive identification of different conformers and the experimental characterization of the intramolecular forces at play which control conformational preferences.

Cabezas, C.; Mata, S.; López, J. C.; Alonso, J. L.

2011-06-01

223

Multiscale Aspects of Modeling Gas-Phase Nanoparticle Synthesis  

PubMed Central

Aerosol reactors are utilized to manufacture nanoparticles in industrially relevant quantities. The development, understanding and scale-up of aerosol reactors can be facilitated with models and computer simulations. This review aims to provide an overview of recent developments of models and simulations and discuss their interconnection in a multiscale approach. A short introduction of the various aerosol reactor types and gas-phase particle dynamics is presented as a background for the later discussion of the models and simulations. Models are presented with decreasing time and length scales in sections on continuum, mesoscale, molecular dynamics and quantum mechanics models. PMID:23729992

Buesser, B.; Grohn, A.J.

2013-01-01

224

Raman study of vibrational dynamics of aminopropylsilanetriol in gas phase  

NASA Astrophysics Data System (ADS)

Raman spectrum of aminopropylsilanetriol (APST) in gas phase has been recorded at room temperature in macro chamber utilizing two-mirror technique over the sample tube. Unlike predominantly trans molecular conformation in condensed phase, the spectra of vapor show that the molecules are solely in gauche conformation with intramolecular hydrogen bond N⋯Hsbnd O which reduces the molecular energy in respect to trans conformation by 0.152 eV. The assignment of the molecular spectra based on the DFT calculation is presented. The strong vibrational bands at 354 cm-1, 588 cm-1 and 3022 cm-1 are proposed for verifying the existence of the ring like, hydrogen bonded structure. Special attention was devoted to the high frequency region, where hydrogen bond vibrations are coupled to stretchings of amino and silanol groups.

Volovšek, V.; Danani?, V.; Bistri?i?, L.; Movre Šapi?, I.; Furi?, K.

2014-01-01

225

A FIRE-ACE/SHEBA Case Study of Mixed-Phase Arctic Boundary Layer Clouds: Entrainment Rate Limitations on Rapid Primary Ice Nucleation Processes  

E-print Network

Limitations on Rapid Primary Ice Nucleation Processes ANN M. FRIDLIND,* BASTIAAN VAN DIEDENHOVEN,1 ANDREW S # National Center for Atmospheric Research, Boulder, Colorado @ Rosenstiel School of Marine and Atmospheric distributions and cloud radar reflectivities with rapidly consumed IN in this case, the measured above-cloud NIN

Shupe, Matthew

226

Diamond nucleation using polyethene  

DOEpatents

The invention presents a simple, non-destructive and non-abrasive method of diamond nucleation using polyethene. It particularly describes the nucleation of diamond on an electrically viable substrate surface using polyethene via chemical vapor deposition (CVD) technique in a gaseous environment.

Morell, Gerardo; Makarov, Vladimir; Varshney, Deepak; Weiner, Brad

2013-07-23

227

Nucleation and Stabilization of Carbon-rich Structures in Interstellar Media  

NASA Astrophysics Data System (ADS)

We study the conditions under which carbon clusters of different sizes form and stabilize. We describe the approach to equilibrium by simulating tenuous carbon gas dynamics to long times. First, we use reactive molecular dynamics simulations to describe the nucleation of long chains, large clusters, and complex cage structures in carbon- and hydrogen-rich interstellar gas phases. We study how temperature, particle density, the presence of hydrogen, and carbon inflow affect the nucleation of molecular moieties with different characteristics, in accordance with astrophysical conditions. We extend the simulations to densities that are orders of magnitude lower than current laboratory densities, to temperatures that are relevant to circumstellar environments of planetary nebulae, and microsecond formation times. We correlate cluster size distributions from the simulations with thermodynamic equilibrium at low temperatures and gas densities, where entropy plays a significant role.

Patra, N.; Král, P.; Sadeghpour, H. R.

2014-04-01

228

Partitioning of organic aerosol components between gas phase and particulate phase  

NASA Astrophysics Data System (ADS)

To understand the role of organics in aerosols both the particulate composition and the gas/vapor phase composition must determined simultaneously. Ammonium sulfates and dicarboxylic acids are major components of continental, tropospheric aerosols. We performed two experiments in which we studied the partitioning of organic aerosol components between the gas and the particulate phase. As model systems we chose (NH4HSO_4 + glutaric acid) aerosol and ((NH4)HSO_4 + methyl glyoxal) aerosol (an oxidation product of isoprene). The experiment were performed in the large Aerosol Chamber at the FZ-Jülich at room temperature. The relative humidity was constantly increased in the course of the experiment (40 -> 90% r.h., 60 -> 90% r.h.).\

Folkers, M.; Mentel, T. F.; Henk, H.; Tillmann, R.; Wahner, A.; Otjes, R. P.; Blom, M. J.; ten Brink, H. M.

2003-12-01

229

Contrail formation: Homogeneous nucleation of H2SO4\\/H2O droplets  

Microsoft Academic Search

Homogeneous nucleation of sub-nanometer H2SO4\\/H2O germs, their growth and freezing probability in the cooling wake of a subsonic jet aircraft at tropopause altitude are investigated. Heteromolecular condensation, water uptake, and coagulation cause a small subset of the germs to grow into nm-sized solution droplets which overcome the Kelvin barrier. These droplets efficiently take up water vapor from the gas phase,

B. Kaercher; Th. Peter; R. Ottmann

1995-01-01

230

Photochemical fine particle formation in the gas phase from acrolein by a two-photon process  

Microsoft Academic Search

Upon exposure to N2 laser light, sedimentary aerosol particles of polyacrolein were produced from gaseous acrolein (AC) in the vapor phase. The nucleation process of aerosol particle formation was investigated by measuring He–Ne laser light intensity scattered by growing aerosol particles which were formed under irradiation with N2 laser light. Scattered light intensity was strongly dependent on N2 laser light

Hiroshi Morita; Katsuhiko Semba; Takeshi Umezawa; Makoto Kuwamura

1999-01-01

231

Gas-Phase Fragmentation Analysis of Nitro-Fatty Acids  

NASA Astrophysics Data System (ADS)

Nitro-fatty acids are electrophilic signaling mediators formed in increased amounts during inflammation by nitric oxide and nitrite-dependent redox reactions. A more rigorous characterization of endogenously-generated species requires additional understanding of their gas-phase induced fragmentation. Thus, collision induced dissociation (CID) of nitroalkane and nitroalkene groups in fatty acids were studied in the negative ion mode to provide mass spectrometric tools for their structural characterization. Fragmentation of nitroalkanes occurred mainly through loss of the NO{2/-} anion or neutral loss of HNO2. The CID of nitroalkenes proceeds via a more complex cyclization, followed by fragmentation to nitrile and aldehyde products. Gas-phase fragmentation of nitroalkene functional groups with additional ? or ? unsaturation occurred through a multiple step cyclization reaction process, leading to 5 and 6 member ring heterocyclic products and carbon chain fragmentation. Cyclization products were not obtained during nitroalkane fragmentation, highlighting the role of double bond ? electrons during NO{2/-} rearrangements, stabilization and heterocycle formation. The proposed structures, mechanisms and products of fragmentation are supported by analysis of 13C and 15N labeled parent molecules, 6 different nitroalkene positional isomers, 6 nitroalkane positional isomers, accurate mass determinations at high resolution and quantum mechanics calculations. Multiple key diagnostic ion fragments were obtained through this analysis, allowing for the precise placement of double bonds and sites of fatty acid nitration, thus supporting an ability to predict nitro positions in biological samples.

Bonacci, Gustavo; Asciutto, Eliana K.; Woodcock, Steven R.; Salvatore, Sonia R.; Freeman, Bruce A.; Schopfer, Francisco J.

2011-09-01

232

Closed-cage tungsten oxide clusters in the gas phase.  

PubMed

During the course of a study on the clustering of W-Se and W-S mixtures in the gas phase using laser desorption ionization (LDI) mass spectrometry, we observed several anionic W-O clusters. Three distinct species, W(6)O(19)(-), W(13)O(29)(-), and W(14)O(32)(-), stand out as intense peaks in the regular mass spectral pattern of tungsten oxide clusters suggesting unusual stabilities for them. Moreover, these clusters do not fragment in the postsource decay analysis. While trying to understand the precursor material, which produced these clusters, we found the presence of nanoscale forms of tungsten oxide. The structure and thermodynamic parameters of tungsten clusters have been explored using relativistic quantum chemical methods. Our computed results of atomization energy are consistent with the observed LDI mass spectra. The computational results suggest that the clusters observed have closed-cage structure. These distinct W(13) and W(14) clusters were observed for the first time in the gas phase. PMID:20377209

Singh, D M David Jeba; Pradeep, T; Thirumoorthy, Krishnan; Balasubramanian, Krishnan

2010-05-01

233

Nahoon: Time-dependent gas-phase chemical model  

NASA Astrophysics Data System (ADS)

Nahoon is a gas-phase chemical model that computes the chemical evolution in a 1D temperature and density structure. It uses chemical networks downloaded from the KInetic Database for Astrochemistry (KIDA) but the model can be adapted to any network. The program is written in Fortran 90 and uses the DLSODES (double precision) solver from the ODEPACK package to solve the coupled stiff differential equations. The solver computes the chemical evolution of gas-phase species at a fixed temperature and density and can be used in one dimension (1D) if a grid of temperature, density, and visual extinction is provided. Grains, both neutral and negatively charged, and electrons are considered as chemical species and their concentrations are computed at the same time as those of the other species. Nahoon contains a test to check the temperature range of the validity of the rate coefficients and avoid extrapolations outside this range. A test is also included to check for duplication of chemical reactions, defined over complementary ranges of temperature.

Wakelam, V.

2014-09-01

234

Engine exhaust particulate and gas phase contributions to vascular toxicity.  

PubMed

Cardiovascular health effects of near-roadway pollution appear more substantial than other sources of air pollution. The underlying cause of this phenomenon may simply be concentration-related, but the possibility remains that gases and particulate matter (PM) may physically interact and further enhance systemic vascular toxicity. To test this, we utilized a common hypercholesterolemic mouse model (Apolipoprotein E-null) exposed to mixed vehicle emission (MVE; combined gasoline and diesel exhausts) for 6?h/d?×?50?d, with additional permutations of removing PM by filtration and also removing gaseous species from PM by denudation. Several vascular bioassays, including matrix metalloproteinase-9 protein, 3-nitrotyrosine and plasma-induced vasodilatory impairments, highlighted that the whole emissions, containing both particulate and gaseous components, was collectively more potent than MVE-derived PM or gas mixtures, alone. Thus, we conclude that inhalation of fresh whole emissions induce greater systemic vascular toxicity than either the particulate or gas phase alone. These findings lend credence to the hypothesis that the near-roadway environment may have a more focused public health impact due to gas-particle interactions. PMID:24730681

Campen, Matthew; Robertson, Sarah; Lund, Amie; Lucero, Joann; McDonald, Jacob

2014-05-01

235

Surfactants from the gas phase may promote cloud droplet formation  

PubMed Central

Clouds, a key component of the climate system, form when water vapor condenses upon atmospheric particulates termed cloud condensation nuclei (CCN). Variations in CCN concentrations can profoundly impact cloud properties, with important effects on local and global climate. Organic matter constitutes a significant fraction of tropospheric aerosol mass, and can influence CCN activity by depressing surface tension, contributing solute, and influencing droplet activation kinetics by forming a barrier to water uptake. We present direct evidence that two ubiquitous atmospheric trace gases, methylglyoxal (MG) and acetaldehyde, known to be surface-active, can enhance aerosol CCN activity upon uptake. This effect is demonstrated by exposing acidified ammonium sulfate particles to 250 parts per billion (ppb) or 8 ppb gas-phase MG and/or acetaldehyde in an aerosol reaction chamber for up to 5 h. For the more atmospherically relevant experiments, i.e., the 8-ppb organic precursor concentrations, significant enhancements in CCN activity, up to 7.5% reduction in critical dry diameter for activation, are observed over a timescale of hours, without any detectable limitation in activation kinetics. This reduction in critical diameter enhances the apparent particle hygroscopicity up to 26%, which for ambient aerosol would lead to cloud droplet number concentration increases of 8–10% on average. The observed enhancements exceed what would be expected based on Köhler theory and bulk properties. Therefore, the effect may be attributed to the adsorption of MG and acetaldehyde to the gas–aerosol interface, leading to surface tension depression of the aerosol. We conclude that gas-phase surfactants may enhance CCN activity in the atmosphere. PMID:23382211

Sareen, Neha; Schwier, Allison N.; Lathem, Terry L.; Nenes, Athanasios; McNeill, V. Faye

2013-01-01

236

Partitioning of hydrogen peroxide between the gas and liquid phases in the presence of surfactant  

Microsoft Academic Search

Gas–liquid phase partitioning is a key physical property that can predict the environmental fate of a compound between two phases. Several environmental factors have been known to affect the gas–liquid phase partitioning. We investigated the influence of surfactant on the gas–liquid phase partitioning of hydrogen peroxide (H2O2). The surfactant used was ammonium perfluorooctanoate (APFO). H2O2 solution containing the surfactant was

Youn-Joo An; Ji Hoon Lee; Seung-Woo Jeong

2007-01-01

237

Multicomponent Dynamical Nucleation Theory And Sensitivity Analysis  

SciTech Connect

Vapor to liquid multi-component nucleation is a dynamical process governed by a delicate interplay between condensation and evaporation. Since the population of the vapor phase is dominated by monomers at reasonable supersaturations, the formation of clusters is governed by monomer association and dissociation reactions. Since no potential energy barrier exists the formation of a cluster is impeded by a free energy of activation that is entropic in nature. Dynamical Nucleation Theory provides a framework in which equilibrium evaporation rate constants can be calculated and the corresponding condensation rate constants determined from detailed balance. The nucleation rate can then be obtained by solving the kinetic equations. The rate constants governing the multi-step kinetics of multi-component nucleation including sensitivity analysis and the influence of possible contaminants will be presented and discussed.

Kathmann, Shawn M.; Schenter, Gregory K.; Garrett, Bruce C.

2004-01-01

238

Deposition nucleation viewed as homogeneous or immersion freezing in pores and cavities  

NASA Astrophysics Data System (ADS)

Heterogeneous ice nucleation is an important mechanism for the glaciation of mixed phase clouds and may also be relevant for cloud formation and dehydration at the cirrus cloud level. It is thought to proceed through different mechanisms, namely contact, condensation, immersion and deposition nucleation. Conceptually, deposition nucleation is the only pathway that does not involve liquid water, but occurs by direct water vapor deposition onto a surface. This study challenges this classical view by putting forward the hypothesis that what is called deposition nucleation is in fact pore condensation and freezing (PCF) occurring in voids and cavities that may form between aggregated primary particles and host water at relative humidity RHw < 100% because of the inverse Kelvin effect. Homogeneous ice nucleation is expected to occur below 235 K when at least one pore is filled with water. Ice nucleation in pores may also happen in immersion mode but with a lower probability because it requires at least one active site in a water filled pore. Therefore a significant enhancement in ice nucleation efficiency is expected when temperature falls below 235 K. For a deposition nucleation process from water vapor no discontinuous change in ice nucleation efficiency should occur at T = 235 K because no liquid water is involved in this process. Studies on freezing in confinement carried out on mesoporous silica materials such as SBA-15, SBA-16, MCM-41, zeolites and KIT have shown that homogeneous ice nucleation occurs abruptly at T = 230-235 K in pores with diameters (D) of 3.5-4 nm or larger but only gradually at T = 210-230 K in pores with D = 2.5-3.5 nm. Pore analysis of clay minerals shows that kaolinites exhibit pore structures with pore diameters (Dp) of 20-50 nm. The mesoporosity of illites and montmorillonites is characterized by pores with Dp = 2-5 nm. The number and size of pores is distinctly increased in acid treated montmorillonites like K10. Water adsorption isotherms of MCM-41 show that pores with Dp = 3.5-4 nm fill with water at RHw = 56-60% in accordance with an inverse Kelvin effect. Water in such pores should freeze homogeneously for T < 235 K even before relative humidity with respect to ice (RHi) reaches ice saturation. Ice crystal growth by water vapor deposition from the gas phase is therefore expected to set in as soon as RHi > 100%. Pores with D > 7.5 nm fill with water at RHi > 100% for T < 235 K and are likely to freeze homogeneously as soon as they are filled with water. Given the pore structure of clay minerals, PCF should be highly efficient for T < 235 K and may occur at T > 235 K in particles that exhibit active sites for immersion freezing within pores. Most ice nucleation studies on clay minerals and mineral dusts indeed show a strong increase in ice nucleation efficiency when temperature is decreased below 235 K in accordance with PCF and are not explicable by the classical view of deposition nucleation. PCF is probably also the prevailing ice nucleation mechanism below water saturation for glassy, soot, and volcanic ash aerosols. No case could be identified that gives clear evidence of ice nucleation by water vapor deposition onto a solid surface.

Marcolli, C.

2014-02-01

239

Spectroscopic studies of molecular iodine emitted into the gas phase by seaweed  

NASA Astrophysics Data System (ADS)

Time profiles of molecular iodine emissions from seven species of seaweed have been measured at high time resolution (7.5 s) by direct spectroscopic quantification of the gas phase I2 using broadband cavity enhanced absorption spectroscopy. Substantial differences were found between species, both in the amounts of I2 emitted when the plants were exposed to air and in the shapes of their emission time profiles. Two species of kelp, Laminaria digitata and Laminaria hyperborea, were found to be the most potent emitters, producing an intense burst of I2 when first exposed to air. I2 was also observed from Saccharina latissima and Ascophyllum nodosum but in lower amounts and with broader time profiles. I2 mixing ratios from two Fucus species and Dictyopteris membranacea were at or below the detection limit of the present instrument (25 pptv). A further set of experiments investigated the time dependence of I2 emissions and aerosol particle formation when fragments of L. digitata were exposed to desiccation in air, to ozone and to oligoguluronate stress factors. Particle formation occurred in all L. digitata stress experiments where ozone and light were present, subject to the I2 mixing ratios being above certain threshold amounts. Moreover, the particle number concentrations closely tracked variations in the I2 mixing ratios, confirming the results of previous studies that the condensable particle-forming gases derive from the photochemical oxidation of the plant's I2 emissions. This work also supports the theory that particle nucleation in the coastal atmosphere occurs in "hot-spot" regions of locally elevated concentrations of condensable gases: the greatest atmospheric concentrations of I2 and hence of condensable iodine oxides are likely to be above plants of the most efficiently emitting kelp species and localised in time to shortly after these seaweeds are uncovered by a receding tide.

Ball, S. M.; Hollingsworth, A. M.; Humbles, J.; Leblanc, C.; Potin, P.; McFiggans, G.

2009-12-01

240

Spectroscopic studies of molecular iodine emitted into the gas phase by seaweed  

NASA Astrophysics Data System (ADS)

Time profiles of molecular iodine emissions from seven species of seaweed have been measured at high time resolution (7.5 s) by direct spectroscopic quantification of the gas phase I2 using broadband cavity enhanced absorption spectroscopy. Substantial differences were found between species, both in the amounts of I2 emitted when the plants were exposed to air and in the shapes of their emission time profiles. Two species of kelp, Laminaria digitata and Laminaria hyperborea, were found to be the most potent emitters, producing an intense burst of I2 when first exposed to air. I2 was also observed from Saccharina latissima and Ascophyllum nodosum but in lower amounts and with broader time profiles. I2 mixing ratios from two Fucus species and Dictyopteris membranacea were at or below the detection limit of the present instrument (25 pptv). A further set of experiments investigated the time dependence of I2 emissions and aerosol particle formation when fragments of L. digitata were exposed to desiccation in air, to ozone and to oligoguluronate stress factors. Particle formation occurred in all L. digitata stress experiments where ozone and light were present, subject to the I2 mixing ratios being above certain threshold amounts. Moreover, the particle number concentrations closely tracked variations in the I2 mixing ratios, confirming the results of previous studies that the condensable particle-forming gases derive from the photochemical oxidation of the plant's I2 emissions. This work also supports the theory that particle nucleation in the coastal atmosphere occurs in "hot-spot" regions of locally elevated concentrations of condensable gases: the greatest atmospheric concentrations of I2 and hence of condensable iodine oxides are likely to be above plants of the most efficiently emitting kelp species and localised in time to shortly after these seaweeds are uncovered by a receding tide.

Ball, S. M.; Hollingsworth, A. M.; Humbles, J.; Leblanc, C.; Potin, P.; McFiggans, G.

2010-07-01

241

Gas-phase reactions of halogen species of atmospheric importance  

NASA Astrophysics Data System (ADS)

A low-pressure discharge-flow technique, with various optical detection methods, has been used to determine bimolecular rate coefficients for a number of reactions in the gas-phase between OH radicals and organic halogen-containing molecules and between NO3 radicals and the iodine species I2 and I. These experiments have shown that: (1) the reaction of methyl iodide with OH accounts for approximately 2 percent of the removal of CH3I from the troposphere as compared with photolysis; (2) abstraction of I-atoms from a C-I bond by OH is probable in the gas-phase; (3) the halogen-containing anaesthetic substances halothane CF3CClBrH, enflurane CF2HOCF2CFClH, isoflurane CF2HOCClHCF3 and sevoflurane (CF3)2CHOCFH2 have significantly shorter tropospheric lifetimes than the fully halogenated CFCs and halons because of reaction with the OH radical and are thus unlikely to be transported up to the stratosphere where they could contribute to the depletion of ozone. Data obtained for reactions between OH and some 'CFC alternatives' along with measurements of the integrated absorption cross-sections of the compounds in the spectral region 800-1200 cm(exp -1) were used to calculate ozone depletion potentials (ODP) and greenhouse warming potentials relative to CFCl3 for each compound. The study of the reactions between OH and CF3CFBrH and CF2BrH was used to provide a useful first estimate of the environmental acceptability of these compounds in the context of their possible use as replacements for the conventional CFCs. A method was developed to provide a first estimate of the ODP of a halogenated alkane without use of a complicated (and expensive) computer modeling scheme. A reaction between molecular iodine and the nitrate radical in the gas-phase was discovered and the kinetics of this reaction have been studied. No temperature or pressure dependence was observed for the rate of reaction, the rate constant of which was found to be (1.5 +/- 0.5) x 10(exp -12)/cu cm/molecule/s. The reaction between I and NO3 was found to occur at a rate of about 60 percent of the hard-sphere collision frequency for the two species. The rate constant for reaction between I and NO3 was found to be (4.5 +/- 1.9) x 10(exp -10)/cu cm/molecule/s. An upper limit for the heat of formation of IONO2 of (21 +/- 3) kJmol(exp -1) was also derived.

Heard, Anne C.

242

Experiments on Nucleation in Different Flow Regimes  

NASA Technical Reports Server (NTRS)

The vast majority of metallic engineering materials are solidified from the liquid phase. Understanding the solidification process is essential to control microstructure, which in turn, determines the properties of materials. The genesis of solidification is nucleation, where the first stable solid forms from the liquid phase. Nucleation kinetics determine the degree of undercooling and phase selection. As such, it is important to understand nucleation phenomena in order to control solidification or glass formation in metals and alloys. Early experiments in nucleation kinetics were accomplished by droplet dispersion methods. Dilitometry was used by Turnbull and others, and more recently differential thermal analysis and differential scanning calorimetry have been used for kinetic studies. These techniques have enjoyed success; however, there are difficulties with these experiments. Since materials are dispersed in a medium, the character of the emulsion/metal interface affects the nucleation behavior. Statistics are derived from the large number of particles observed in a single experiment, but dispersions have a finite size distribution which adds to the uncertainty of the kinetic determinations. Even though temperature can be controlled quite well before the onset of nucleation, the release of the latent heat of fusion during nucleation of particles complicates the assumption of isothermality during these experiments. Containerless processing has enabled another approach to the study of nucleation kinetics. With levitation techniques it is possible to undercool one sample to nucleation repeatedly in a controlled manner, such that the statistics of the nucleation process can be derived from multiple experiments on a single sample. The authors have fully developed the analysis of nucleation experiments on single samples following the suggestions of Skripov. The advantage of these experiments is that the samples are directly observable. The nucleation temperature can be measured by noncontact optical pyrometry, the mass of the sample is known, and post-processing analysis can be conducted on the sample. The disadvantages are that temperature measurement must have exceptionally high precision, and it is not possible to isolate specific heterogeneous sites as in droplet dispersions. Levitation processing of refractory materials in ultra high vacuum provides an avenue to conduct these kinetic studies on single samples. Two experimental methods have been identified where ultra high vacuum experiments are possible; electrostatic levitation in ground-based experiments and electromagnetic processing in low earth orbit on TEMPUS. Such experiments, reported here, were conducted on zirconium. Liquid zirconium is an excellent solvent and has a high solubility for contaminants contained in the bulk material as well as those contaminants found in the vacuum environment. Oxides, nitrides, and carbides do not exist in the melt, and do not form on the surface of molten zirconium, for the materials and vacuum levels used in this study. Ground-based experiments with electrostatic levitation have shown that the statistical nucleation kinetic experiments are viable and yield results which are consistent with classical nucleation theory. The advantage of low earth orbit experiments is the ability to vary the flow conditions in the liquid prior to nucleation. The put-pose of nucleation experiments in TEMPUS was to examine.

Bayuzick, R. J.; Hofmeister, W. H.; Morton, C. M.; Robinson, M. B.

1998-01-01

243

Musculoskeletal-induced Nucleation in Altitude Decompression Sickness  

NASA Technical Reports Server (NTRS)

Musculoskeletal activity has the potential to both improve and compromise decompression safety. Exercise enhances inert gas elimination during oxygen breathing prior to decompression (prebreathe), but it may also promote bubble nuclei formation (nucleation), which can lead to gas phase separation and bubble growth and increase the risk of decompression sickness (DCS). The timing, pattern and intensity of musculoskeletal activity and the level of tissue supersaturation may be critical to the net effect. There are limited data available to evaluate cost-benefit relationships. Understanding the relationship is important to improve our understanding of the underlying mechanisms of nucleation in exercise prebreathe protocols and to quantify risk in gravity and microgravity environments. Data gathered during NASA's Prebreathe Reduction Program (PRP) studies combined oxygen prebreathe and exercise followed by low pressure (4.3 psi; altitude equivalent of 30,300 ft [9,235 m]) microgravity simulation to produce two protocols used by astronauts preparing for extravehicular activity. Both the Phase II/CEVIS (cycle ergometer vibration isolation system) and ISLE (in-suit light exercise) trials eliminated ambulation to more closely simulate the microgravity environment. The CEVIS results (35 male, 10 female) serve as control data for this NASA/Duke study to investigate the influence of ambulation exercise on bubble formation and the subsequent risk of DCS.

Pollock, N. W.; Natoli, M. J.; Conkin, J.; Wessel, J. H., III; Gernhardt, M. L.

2014-01-01

244

Ice nucleation terminology  

NASA Astrophysics Data System (ADS)

Progress in the understanding of ice nucleation is being hampered by the lack of uniformity in how some terms are used in the literature. This even extends to some ambiguity of meanings attached to some terms. Suggestions are put forward here for common use of terms. Some are already well established and clear of ambiguities. Others are less engrained and will need a conscious effort in adoption. Evolution in the range of systems where ice nucleation is being studied enhances the need for a clear nomenclature. The ultimate limit in the clarity of definitions is, of course, the limited degree to which ice nucleation processes are understood.

Vali, G.; DeMott, P.; Möhler, O.; Whale, T. F.

2014-08-01

245

SCALING PROPERTIES OF THE CRITICAL NUCLEUS IN CLASSICAL AND DENSITY FUNCTIONAL NUCLEATION THEORIES  

E-print Network

SCALING PROPERTIES OF THE CRITICAL NUCLEUS IN CLASSICAL AND DENSITY FUNCTIONAL NUCLEATION THEORIES and bulk condensed phase, flp. . Discrepancies between classical and DF nucleation theories and hetween the classical theory and experiment are interpreted using these resuIts. Keywords- Nucleation. Clusters, Phase

246

New approaches to understanding the mechanism of nucleate boiling: Insights into an old problem.  

E-print Network

New approaches to understanding the mechanism of nucleate boiling: Insights into an old problem conductivity than the liquid heated from below as a model system for nucleate boiling. A quasisteady continuum-phase system and find a P-T phase diagram that delineates the boundary between nucleate and film boiling. Under

Lin, Qiao

247

Homogeneous bubble nucleation in rhyolitic melt: Experiments and nonclassical theory  

E-print Network

Homogeneous bubble nucleation in rhyolitic melt: Experiments and nonclassical theory H. M eruptions. The first and most critical step in degassing is the nucleation of gas bubbles, which requires bubble number densities in pyroclasts. We provide a potential resolution to this problem through

Gonnermann, Helge

248

Infrared photodissociation spectroscopy of protonated neurotransmitters in the gas phase  

NASA Astrophysics Data System (ADS)

Protonated neurotransmitters have been produced in the gas phase via a novel photochemical scheme: complexes of the species of interest, 1-phenylethylamine, 2-amino-1-phenylethanol and the diastereo-isomers, ephedrine and pseudoephedrine, with a suitable proton donor, phenol (or indole), are produced in a supersonic expansion and ionized by resonant two photon ionization of the donor. Efficient proton transfer generates the protonated neurotransmitters, complexed to a phenoxy radical. Absorption of infrared radiation, and subsequent evaporation of the phenoxy tag, coupled with time of flight mass spectrometry, provides vibrational spectra of the protonated (and also hydrated) complexes for comparison with the results of quantum chemical computation. Comparison with the conformational structures of the neutral neurotransmitters (established previously) reveals the effect of protonation on their structure. The photochemical proton transfer strategy allows spectra to be recorded from individual laser shots and their quality compares favourably with that obtained using electro-spray or matrix assisted laser desorption ion sources.

MacLeod, N. A.; Simons, J. P.

2007-03-01

249

Gas-Phase Infrared Spectrum of the Coronene Cation  

NASA Astrophysics Data System (ADS)

The gas-phase infrared spectrum of the coronene cation in the 700-1700 cm-1 range is presented. The spectrum is obtained via multiphoton dissociation spectroscopy of ionic coronene stored in a quadrupole ion trap using the intense and narrowband infrared radiation of a free electron laser. The spectrum shows main absorption peaks at 849, 1327, and 1533 cm-1 along with some weak and barely resolved features, in good agreement with density functional calculations if the effects of vibrational anharmonicity are accounted for. Relative line intensities show remarkable differences with respect to matrix isolation data. The novel experimental technique applied here leads in a natural way to an absorption spectrum of highly excited species. Hence, measured absorption spectra can be compared rather directly to interstellar emission spectra, negating to some extent the need for detailed model calculations.

Oomens, Jos; Sartakov, Boris G.; Tielens, A. G. G. M.; Meijer, Gerard; von Helden, Gert

2001-10-01

250

Regenerable Air Purification System for Gas-Phase Contaminant Control  

NASA Technical Reports Server (NTRS)

A regenerable air purification system (RAPS) that uses water vapor to displace adsorbed contaminants from an. adsorbent column into a closed oxidation loop is under development through cooperative R&D between Vanderbilt University and NASA Ames Research Center. A unit based on this design can be used for removing trace gas-phase contaminants from spacecraft cabin air or from polluted process streams including incinerator exhaust. Recent work has focused on fabrication and operation of a RAPS breadboard at NASA Ames, and on measurement of adsorption isotherm data for several important organic compounds at Vanderbilt. These activities support the use and validation of RAPS modeling software also under development at Vanderbilt, which will in turn be used to construct a prototype system later in the project.

Constantinescu, Ileana C.; Qi, Nan; LeVan, M. Douglas; Finn, Cory K.; Finn, John E.; Luna, Bernadette (Technical Monitor)

2000-01-01

251

Gas-phase synthesis of magnetic metal/polymer nanocomposites.  

PubMed

Highly magnetic metal Co nanoparticles were produced via reducing flame spray pyrolysis, and directly coated with an epoxy polymer in flight. The polymer content in the samples varied between 14 and 56 wt% of nominal content. A homogenous dispersion of Co nanoparticles in the resulting nanocomposites was visualized by electron microscopy. The size and crystallinity of the metallic fillers was not affected by the polymer, as shown by XRD and magnetic hysteresis measurements. The good control of the polymer content in the product nanocomposite was shown by elemental analysis. Further, the successful polymerization in the gas phase was demonstrated by electron microscopy and size measurements. The presented effective, dry and scalable one-step synthesis method for highly magnetic metal nanoparticle/polymer composites presented here may drastically decrease production costs and increase industrial yields. PMID:25422410

Starsich, Fabian H L; Hirt, Ann M; Stark, Wendelin J; Grass, Robert N

2014-12-19

252

Silicon Nanowire-Based Devices for Gas-Phase Sensing  

PubMed Central

Since their introduction in 2001, SiNW-based sensor devices have attracted considerable interest as a general platform for ultra-sensitive, electrical detection of biological and chemical species. Most studies focus on detecting, sensing and monitoring analytes in aqueous solution, but the number of studies on sensing gases and vapors using SiNW-based devices is increasing. This review gives an overview of selected research papers related to the application of electrical SiNW-based devices in the gas phase that have been reported over the past 10 years. Special attention is given to surface modification strategies and the sensing principles involved. In addition, future steps and technological challenges in this field are addressed. PMID:24368699

Cao, Anping; Sudholter, Ernst J.R.; de Smet, Louis C.P.M.

2014-01-01

253

Regenerable Air Purification System for Gas-Phase Contaminant Control  

NASA Technical Reports Server (NTRS)

Tests of a pre-prototype regenerable air purification system (RAPS) that uses water vapor to displace adsorbed contaminants from an adsorbent column have been performed at NASA Ames Research Center. A unit based on this design can be used for removing trace gas-phase contaminants from spacecraft cabin air or from polluted process streams including incinerator exhaust. During the normal operation mode, contaminants are removed from the air on the column. Regeneration of the column is performed on-line. During regeneration, contaminants are displaced and destroyed inside the closed oxidation loop. In this presentation we discuss initial experimental results for the performance of RAPS in the removal and treatment of several important spacecraft contaminant species from air.

Constantinescu, Ileana C.; Finn, John E.; LeVan, M. Douglas; Lung, Bernadette (Technical Monitor)

2000-01-01

254

Interfacial process of nucleation and molecular nucleation templator  

NASA Astrophysics Data System (ADS)

Interfacial effects of nucleation inhibition and promotion were identified from the nucleation of paracetamol. Unlike the classic interfacial effects, which are caused by the change in nucleation barrier, the nonepitaxial interfacial effects are only associated with kink integration kinetics. Methylparaben inhibits nucleation by increasing the desolvation free energy barrier, which is revealed as the nonepitaxial interfacial effect of nucleation inhibition. Polysaccharide revealed its nonepitaxial interfacial effects of nucleation promotion by lowering the conformation entropic barrier via liquid molecule preordering. Polysaccharide can be regarded as an example of molecular nucleation promoter based on the nonepitaxial interfacial effects.

Liu, X. Y.

2001-07-01

255

Nucleation and growth of combustion flame deposited diamond coatings on silicon nitride  

NASA Astrophysics Data System (ADS)

An investigation has been performed on the kinetics of diamond nucleation on silicon nitride (Si3N4) based materials during oxy-acetylene combustion flame chemical vapor deposition. The deposits were characterized using scanning electron microscopy (SEM), x-ray diffraction (XRD), x-ray photoelectron spectroscopy (XPS), and atomic force microscopy (AFM) techniques. Kinetic parameters of the nucleation process, such as nucleation rate (I), period of initial nuclei formation (tng), and maximum nucleation density (Nd) were experimentally determined. It was concluded that at low temperatures (Ts < 875°C), the observed nucleation density is due to epitaxial or pseudo-epitaxial growth on residual particles on the substrate surface. At higher temperatures (Ts > 875°C), heterogeneous nucleation of diamond on Si3N4 occurs with an apparent activation energy ( Eahet ) of ˜ 18 kcal/mol. From an Arrhenius plot of particle growth rate, the activation energy (Ea) for diamond growth was calculated to be ˜ 9 kcal/mol. These results suggest that the energy barrier associated with the heterogeneous nucleation process ( Eahet > Ea) may in fact be responsible for the observed low nucleation densities on Si3N4 substrates. Consequently, nucleation density on Si3N4 is limited by the concentration of available sites for nuclei formation. As surface diffusion to those sites was determined to be negligible, growth of stable nuclei occurs via direct impingement of gas phase species. Based on these conclusions, a multistage deposition technique was developed to deposit continuous diamond coatings on untreated Si3N4 substrates. This two stage technique consisted of (i) an in situ flame pretreatment of the substrate to enhance nucleation through the formation of SiC and (ii) subsequent growth on the flame pretreated surface under optimized parameters. Using a previously developed compression test for brittle coating/substrate systems, the adhesion of multistage deposited coatings was compared to conventionally deposited coatings. Normalized values of adhesion for the multistage coatings were observed to be the same order of magnitude as the conventionally seeded diamond coatings. However, the failure mechanisms of the two coatings were observed to be significantly different. Multistage coating failure was characterized by partial ( ˜ typically 5%) delamination while conventionally seeded coatings were observed to completely disintegrate (100% delamination) at failure. Thus, it was projected that the fracture toughness of the multistage deposited coatings may be superior to that of conventionally seeded coatings. Finally, a modified flame technique is introduced to remedy a number of deficiencies and increase the commercial viability of combustion flame synthesis. This technique consists of simple modifications to conventional apparatus which significantly enhances the deposition area and expands the number of candidate substrate materials and geometries that can be coated using combustion flame CVD.

Rozbicki, Robert T.

256

Ab initio kinetics of gas phase decomposition reactions.  

PubMed

The thermal and kinetic aspects of gas phase decomposition reactions can be extremely complex due to a large number of parameters, a variety of possible intermediates, and an overlap in thermal decomposition traces. The experimental determination of the activation energies is particularly difficult when several possible reaction pathways coexist in the thermal decomposition. Ab initio calculations intended to provide an interpretation of the experiment are often of little help if they produce only the activation barriers and ignore the kinetics of the decomposition process. To overcome this ambiguity, a theoretical study of a complete picture of gas phase thermo-decomposition, including reaction energies, activation barriers, and reaction rates, is illustrated with the example of the ?-octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) molecule by means of quantum-chemical calculations. We study three types of major decomposition reactions characteristic of nitramines: the HONO elimination, the NONO rearrangement, and the N-NO(2) homolysis. The reaction rates were determined using the conventional transition state theory for the HONO and NONO decompositions and the variational transition state theory for the N-NO(2) homolysis. Our calculations show that the HMX decomposition process is more complex than it was previously believed to be and is defined by a combination of reactions at any given temperature. At all temperatures, the direct N-NO(2) homolysis prevails with the activation barrier at 38.1 kcal/mol. The nitro-nitrite isomerization and the HONO elimination, with the activation barriers at 46.3 and 39.4 kcal/mol, respectively, are slow reactions at all temperatures. The obtained conclusions provide a consistent interpretation for the reported experimental data. PMID:21077597

Sharia, Onise; Kuklja, Maija M

2010-12-01

257

Gas phase hydrogen permeation in alpha titanium and carbon steels  

NASA Technical Reports Server (NTRS)

Commercially pure titanium and heats of Armco ingot iron and steels containing from 0.008-1.23 w/oC were annealed or normalized and machined into hollow cylinders. Coefficients of diffusion for alpha-Ti and alpha-Fe were determined by the lag-time technique. Steady state permeation experiments yield first power pressure dependence for alpha-Ti and Sievert's law square root dependence for Armco iron and carbon steels. As in the case of diffusion, permeation data confirm that alpha-titanium is subject to at least partial phase boundary reaction control while the steels are purely diffusion controlled. The permeation rate in steels also decreases as the carbon content increases. As a consequence of Sievert's law, the computed hydrogen solubility decreases as the carbon content increases. This decreases in explained in terms of hydrogen trapping at carbide interfaces. Oxidizing and nitriding the surfaces of alpha-titanium membranes result in a decrease in the permeation rate for such treatment on the gas inlet surfaces but resulted in a slight increase in the rate for such treatment on the gas outlet surfaces. This is explained in terms of a discontinuous TiH2 layer.

Johnson, D. L.; Shah, K. K.; Reeves, B. H.; Gadgeel, V. L.

1980-01-01

258

Dynamical Nucleation Theory  

SciTech Connect

Vapor to liquid nucleation is a dynamical process governed by a delicate interplay between condensation and evaporation rates. Since the vapor is comprised essentially of monomers, the formation of clusters is governed by monomer association and dissociation reactions. The formation of a cluster is impeded by a free energy of activation that is entropic in nature since no potential energy barrier exists. Variational transition state theory provides a framework in which equilibrium evaporation rate constants can be calculated and the corresponding condensation rate constants determined from detailed balance. The nucleation rate can then be obtained by solving the pseudo-first order kinetic equations. The rate constants governing the multi-step kinetics of small water cluster nucleation including the possible role of contaminants will be presented. In addition, the limiting behavior of the rate constants and a sensitivity analysis of the steady-state nucleation rate on these rate constants will be discussed.

Kathmann, Shawn M.; Schenter, Gregory K.; Garrett, Bruce C.; B. Hale and M. Kulmala

2000-01-01

259

Thermo-elastic aspects of dynamic nucleation  

NASA Astrophysics Data System (ADS)

In spite of recent progress in our understanding of the absolute stability of elastic phases under loads, the generic presence of metastable configurations and the possibility of their dynamic breakdown remains a major problem in the mechanical theory of phase transitions in solids. In this paper, by considering the simplest one-dimensional model, we study the interplay between inertial and thermal effects associated with nucleation of a new phase, and address the crucial question concerning the size of a perturbation breaking metastability. We begin by reformulating the nucleation problem as a degenerate Riemann problem. By choosing a specific kinetic relation, originating from thermo-visco-capillary (TVC) regularization, we solve a self-similar problem analytically and demonstrate the existence of two types of solutions: with nucleation and without it. We then show that in the presence of a non-zero latent heat, solution with nucleation may by itself be non-unique. To understand the domain of attraction of different self-similar solutions with and without nucleation, we regularize the model and study numerically the full scale initial value problem with locally perturbed data. Through numerical experiments we present evidence that the TVC regularization is successful in removing deficiencies of the classical thermo-elastic model and is sufficient in specifying the limits of metastability.

Ngan, S.-C.; Truskinovsky, L.

2002-06-01

260

Full field gas phase velocity measurements in microgravity  

NASA Technical Reports Server (NTRS)

Measurement of full-field velocities via Particle Imaging Velocimetry (PIV) is common in research efforts involving fluid motion. While such measurements have been successfully performed in the liquid phase in a microgravity environment, gas-phase measurements have been beset by difficulties with seeding and laser strength. A synthesis of techniques developed at NASA LeRC exhibits promise in overcoming these difficulties. Typical implementation of PIV involves forming the light from a pulsed laser into a sheet that is some fraction of a millimeter thick and 50 or more millimeters wide. When a particle enters this sheet during a pulse, light scattered from the particle is recorded by a detector, which may be a film plane or a CCD array. Assuming that the particle remains within the boundaries of the sheet for the second pulse and can be distinguished from neighboring particles, comparison of the two images produces an average velocity vector for the time between the pulses. If the concentration of particles in the sampling volume is sufficiently large but the particles remain discrete, a full field map may be generated.

Griffin, Devon W.; Yanis, William

1995-01-01

261

Breakdown of a topological phase: quantum phase transition in a loop gas model with tension.  

PubMed

We study the stability of topological order against local perturbations by considering the effect of a magnetic field on a spin model--the toric code--which is in a topological phase. The model can be mapped onto a quantum loop gas where the perturbation introduces a bare loop tension. When the loop tension is small, the topological order survives. When it is large, it drives a continuous quantum phase transition into a magnetic state. The transition can be understood as the condensation of "magnetic" vortices, leading to confinement of the elementary "charge" excitations. We also show how the topological order breaks down when the system is coupled to an Ohmic heat bath and relate our results to error rates for topological quantum computations. PMID:17359006

Trebst, Simon; Werner, Philipp; Troyer, Matthias; Shtengel, Kirill; Nayak, Chetan

2007-02-16

262

Breakdown of a topological phase: Quantum phase transition in a loop gas model with tension  

E-print Network

We study the stability of topological order against local perturbations by considering the effect of a magnetic field on a spin model -- the toric code -- which is in a topological phase. The model can be mapped onto a quantum loop gas where the perturbation introduces a bare loop tension. When the loop tension is small, the topological order survives. When it is large, it drives a continuous quantum phase transition into a magnetic state. The transition can be understood as the condensation of `magnetic' vortices, leading to confinement of the elementary `charge' excitations. We also show how the topological order breaks down when the system is coupled to an Ohmic heat bath and discuss our results in the context of quantum computation applications.

Simon Trebst; Philipp Werner; Matthias Troyer; Kirill Shtengel; Chetan Nayak

2006-09-03

263

Gas-Phase Reactions of Halogen Species of Atmospheric Importance.  

NASA Astrophysics Data System (ADS)

Available from UMI in association with The British Library. Requires signed TDF. A low-pressure discharge-flow technique, with various optical detection methods, has been used to determine bimolecular rate coefficients for a number of reactions in the gas-phase between OH radicals and organic halogen -containing molecules and between NO_3 radicals and the iodine species I_2 and I. These experiments have shown that: (i) the reaction of methyl iodide with OH accounts for approximately 2% of the removal of CH_3I from the troposphere as compared with photolysis; (ii) abstraction of I-atoms from a C-I bond by OH is probable in the gas -phase; (iii) the halogen-containing anaesthetic substances halothane CF_3CCl BrH, enflurane CF_2HOCF _2CFClH, isoflurane CF_2HOCClHCF _3 and sevoflurane (CF_3) _2CHOCFH_2 have significantly shorter tropospheric lifetimes than the fully halogenated CFCs and halons because of reaction with the OH radical and are thus unlikely to be transported up to the stratosphere where they could contribute to the depletion of ozone. Data obtained for reactions between OH and some 'CFC alternatives' along with measurements of the integrated absorption cross -sections of the compounds in the spectral region 800-1200 cm^{-1} were used to calculate ozone depletion potentials (ODP) and greenhouse warming potentials relative to CFCl_3 for each compound. The study of the reactions between OH and CF_3CFBrH and CF _2BrH was used to provide a useful first estimate of the environmental acceptability of these compounds in the context of their possible use as replacements for the conventional CFCs. A method was developed to provide a first estimate of the ODP of a halogenated alkane without use of a complicated (and expensive) computer modeling scheme. A reaction between molecular iodine and the nitrate radical in the gas-phase was discovered and the kinetics of this reaction have been studied. No temperature or pressure dependence was observed for the rate of reaction, the rate constant of which was found to be (1.5 +/- 0.5) times 10 ^{-12}cm^{ -3}molecule^{-1}s ^{-1}. The reaction between I and NO_3 was found to occur at a rate of about 60% of the hard-sphere collision frequency for the two species. The rate constant for reaction between I and NO_3 was found to be (4.5 +/- 1.9) times 10^{-10}cm^3 molecule^{-1}s ^{-1}. An upper limit for the heat of formation of IONO_2 of (21 +/- 3) kJmol^ {-1} was also derived. (Abstract shortened by UMI.).

Heard, Anne C.

264

Nucleation of protein fibrillation by nanoparticles.  

PubMed

Nanoparticles present enormous surface areas and are found to enhance the rate of protein fibrillation by decreasing the lag time for nucleation. Protein fibrillation is involved in many human diseases, including Alzheimer's, Creutzfeld-Jacob disease, and dialysis-related amyloidosis. Fibril formation occurs by nucleation-dependent kinetics, wherein formation of a critical nucleus is the key rate-determining step, after which fibrillation proceeds rapidly. We show that nanoparticles (copolymer particles, cerium oxide particles, quantum dots, and carbon nanotubes) enhance the probability of appearance of a critical nucleus for nucleation of protein fibrils from human beta(2)-microglobulin. The observed shorter lag (nucleation) phase depends on the amount and nature of particle surface. There is an exchange of protein between solution and nanoparticle surface, and beta(2)-microglobulin forms multiple layers on the particle surface, providing a locally increased protein concentration promoting oligomer formation. This and the shortened lag phase suggest a mechanism involving surface-assisted nucleation that may increase the risk for toxic cluster and amyloid formation. It also opens the door to new routes for the controlled self-assembly of proteins and peptides into novel nanomaterials. PMID:17485668

Linse, Sara; Cabaleiro-Lago, Celia; Xue, Wei-Feng; Lynch, Iseult; Lindman, Stina; Thulin, Eva; Radford, Sheena E; Dawson, Kenneth A

2007-05-22

265

Trimethylsilyl derivatization of nucleic acid anions in the gas phase  

NASA Astrophysics Data System (ADS)

Ion-molecule reactions between nucleic acid anions, [M-nH]n, formed via electrospray ionization, and trimethylsilylchloride have been investigated in an ion trap mass spectrometer at a helium bath gas pressure of 1 mtorr. Three types of reactions are observed: (i) SN2(Si) when n > 1 ; (ii) adduct formation when n = 1 ; and (iii) addition followed by elimination of HCl when n = 1 and where an acidic phosphate proton is present (e.g., 5'-pdA). The kinetics of these reactions have been studied for various anions derived from the following deoxyadenosine species: 5'-pdA; 5'-pppdA, 5'-d(AA)-3'; 5'-d(AAA)-3' and 5'-d(AAAA)-3'. The following reactivity order is observed: [M-2H]2- of 5'-pppdA > [M-2H]2- of 5'-d(AAA)-3' > [M-3H]3- of 5'-d(AAAA)-3' > [M-3H + TMS]2- of 5'-d(AAAA)-3' > [M-2H]2- of 5'-d(AAAA)-3' > [M-H]- of 5'-pdA >> [M-H]- of 5'-d(AA)-3' > [M-H]- of 5'-d(AAA)-3'. In addition, the collision-induced dissociation reactions of the products of these reactions have been studied. Decomposition reactions are consistent with trimethylsilyl attachment on the phosphodiester linkage(s) in oligonucleotides and on the phosphate moieties of 5'-pdA and 5'-pppdA. Comparison of data acquired for modified and unmodified oligonucleotide anions of the same charge state reveal that TMS modification can significantly alter the favored dissociation channels, giving rise to sequence information. The results suggest that gas phase TMS derivatization of oligonucleotide anions, combined with tandem mass spectrometry, can provide sequence information complementary to that derived from unmodified anions.

O'Hair, Richard A. J.; McLuckey, Scott A.

1997-03-01

266

Fragile-to-fragile liquid transition at Tg and stable-glass phase nucleation rate maximum at the Kauzmann temperature TK  

NASA Astrophysics Data System (ADS)

An undercooled liquid is unstable. The driving force of the glass transition at Tg is a change of the undercooled-liquid Gibbs free energy. The classical Gibbs free energy change for a crystal formation is completed including an enthalpy saving. The crystal growth critical nucleus is used as a probe to observe the Laplace pressure change ?p accompanying the enthalpy change -Vm×?p at Tg where Vm is the molar volume. A stable glass-liquid transition model predicts the specific heat jump of fragile liquids at T?Tg, the Kauzmann temperature TK where the liquid entropy excess with regard to crystal goes to zero, the equilibrium enthalpy between TK and Tg, the maximum nucleation rate at TK of superclusters containing magic atom numbers, and the equilibrium latent heats at Tg and TK. Strong-to-fragile and strong-to-strong liquid transitions at Tg are also described and all their thermodynamic parameters are determined from their specific heat jumps. The existence of fragile liquids quenched in the amorphous state, which do not undergo liquid-liquid transition during heating preceding their crystallization, is predicted. Long ageing times leading to the formation at TK of a stable glass composed of superclusters containing up to 147 atom, touching and interpenetrating, are evaluated from nucleation rates. A fragile-to-fragile liquid transition occurs at Tg without stable-glass formation while a strong glass is stable after transition.

Tournier, Robert F.

2014-12-01

267

An algorithm for semi-empirical design of nucleation rate surface.  

PubMed

During the last half of century, Classical Nucleation Theory (CNT) has been developed and there have been advances in the molecular theory of nucleation. Most of these efforts have been directed towards small molecule system modeling using intermolecular potentials. Summarizing the nucleation theory, it can be concluded that the current theory is far from complete. Agreement is generally not obtained between experimental and theoretical results. In practical applications, parametric theories can be used for the systems of interest. However, experimental measurements are still the best source of information on nucleation. Experiments are labor intensive and costly, and thus, it is useful to extend the value of limited experimental measurements to a broader range of nucleation conditions. The available nucleation parameters represent only small regions of possible nucleation conditions over the range from the critical temperature to absolute zero. Thus, it is useful to develop better tools to use the data to estimate semi-empirical nucleation rate surfaces. Following our published approach, the nucleation rate surface for any system can be constructed over its phase diagram. This concept involves using the phase equilibrium diagram to establish lines of zero nucleation rates. Nucleation rate surfaces arise from equilibrium lines and their extensions that are representing unstable equilibria. Only limited experimental data is available for use in normalizing the slopes of the linearized nucleation rate surfaces. The nucleation rate surface is described in terms of steady-state nucleation rates. To design the surfaces of nucleation rates, several assumptions are presented. In the present study, an algorithm for the semi-empirical design of nucleation rate surfaces is introduced. The topology of the nucleation rate surface for a unary system using the example of water vapor nucleation is created semi-empirically. The nucleation of two concurrent (stable and unstable) phase states of critical embryos is considered in the context of multi-surface nucleation rates. Only one phase transition (melting) in the condensed state of water is considered for simplicity. The nucleation rate surface is constructed numerically using the available experimental results for vapor nucleation and phase diagram for water. The nucleation rate for water vapor is developed for the full temperature interval, i.e. from critical point to absolute zero. The results help to suggest a new direction for experimental nucleation research. PMID:16122546

Anisimova, Lyubov; Anisimov, Michael; Semin, George; Turner, Peter; Hopke, Philip K

2005-10-01

268

Pressure drop, heat transfer, critical heat flux, and flow stability of two-phase flow boiling of water and ethylene glycol/water mixtures - final report for project "Efficent cooling in engines with nucleate boiling."  

SciTech Connect

Because of its order-of-magnitude higher heat transfer rates, there is interest in using controllable two-phase nucleate boiling instead of conventional single-phase forced convection in vehicular cooling systems to remove ever increasing heat loads and to eliminate potential hot spots in engines. However, the fundamental understanding of flow boiling mechanisms of a 50/50 ethylene glycol/water mixture under engineering application conditions is still limited. In addition, it is impractical to precisely maintain the volume concentration ratio of the ethylene glycol/water mixture coolant at 50/50. Therefore, any investigation into engine coolant characteristics should include a range of volume concentration ratios around the nominal 50/50 mark. In this study, the forced convective boiling heat transfer of distilled water and ethylene glycol/water mixtures with volume concentration ratios of 40/60, 50/50, and 60/40 in a 2.98-mm-inner-diameter circular tube has been investigated in both the horizontal flow and the vertical flow. The two-phase pressure drop, the forced convective boiling heat transfer coefficient, and the critical heat flux of the test fluids were determined experimentally over a range of the mass flux, the vapor mass quality, and the inlet subcooling through a new boiling data reduction procedure that allowed the analytical calculation of the fluid boiling temperatures along the experimental test section by applying the ideal mixture assumption and the equilibrium assumption along with Raoult's law. Based on the experimental data, predictive methods for the two-phase pressure drop, the forced convective boiling heat transfer coefficient, and the critical heat flux under engine application conditions were developed. The results summarized in this final project report provide the necessary information for designing and implementing nucleate-boiling vehicular cooling systems.

Yu, W.; France, D. M.; Routbort, J. L. (Energy Systems)

2011-01-19

269

The Gas-Phase Spectra of the 1-INDANYL Radical  

NASA Astrophysics Data System (ADS)

The gas-phase resonant two color two photon ionization (R2C2PI) spectrum of the 1-indanyl radical (m/z=117) has been identified in the region 20800 - 22600 cm^{-1} in a molecular beam. The radical was produced from the discharge of ˜1 % indene in Argon . Laser induced fluorescence (LIF) spectra were recorded in the same region revealing those features observed in R2C2PI. Other precursor molecules were investigated and it was found that the indane precursor resulted in the strongest signal. The fluorescence of the 1-indanyl radical origin band (21158 cm^{-1}) was dispersed in order to determine the ground state vibrational energies. The dispersed fluorescence (DF) spectrum is consistent with the previously observed condensed-phase emission spectrum of the 1-indanyl radical. The DF values were compared with those ground state energies determined by DFT. Franck-Condon factors computed based on the ab initio results showed good agreement with the observed spectrum. Based on the theoretical results we assigned the observed bands. The LIF spectrum contained other bands inconsistent with the 1-indanyl radical. These have been determined to be carried by 1-phenylpropargyl radical and another currently unknown radical determined by R2C2PI to have m/z=133. [1] T. Izumida, K. Inoue, S. Noda, and H. Yoshida, Bull. Chem. Soc. Jpn. 54, 2517 (1981). [2] N. J. Reilly, D. L. Kokkin, M. Nakajima, K. Nauta, S. H. Kable, and T. W. Schmidt, J. Am. Chem. Soc. 130, 3137 (2009).

Troy, Tyler P.; Nakajima, Masakazu; Chalyavi, Nahid; Clady, Raphaël G. C. R.; Nauta, Klaas; Kable, Scott H.; Schmidt, Timothy W.

2009-06-01

270

Classical Heisenberg lattice-gas model: Thermodynamics and phase diagrams  

NASA Astrophysics Data System (ADS)

The present paper addresses a simple lattice gas model, consisting of particles that carry a three-component classical spin (i.e., a three-component unit vector), and associated with a simple-cubic lattice; each site can host one particle at most, thus implicitly allowing for hard-core repulsion; the pair interaction, restricted to nearest neighbors, is ferromagnetic and isotropic in spin space. We have studied thermodynamic properties and phase diagrams of the model by means of mean-field and two-site cluster treatments, and identified the tricritical points. Note that the fluctuating occupation numbers give rise to additional fluidlike observables in comparison with the usual saturated-lattice situation. The case of zero chemical potential has been investigated by grand-canonical Monte Carlo simulations, so as to obtain a quantitative test of the named approximations, as well as a more detailed physical characterization. The mean-field treatment was found to yield only qualitative agreement with simulation results, and the two-site cluster treatment recognizably improved upon it. Extensive simulations point to a second-order transition, whose universality class was found to be the same as its saturated-lattice counterpart.

Chamati, Hassan; Romano, Silvano

2005-08-01

271

Gas phase production and loss of isoprene epoxydiols.  

PubMed

Isoprene epoxydiols (IEPOX) form in high yields from the OH-initiated oxidation of isoprene under low-NO conditions. These compounds contribute significantly to secondary organic aerosol formation. Their gas-phase chemistry has, however, remained largely unexplored. In this study, we characterize the formation of IEPOX isomers from the oxidation of isoprene by OH. We find that cis-?- and trans-?-IEPOX are the dominant isomers produced, and that they are created in an approximate ratio of 1:2 from the low-NO oxidation of isoprene. Three isomers of IEPOX, including cis-?- and trans-?, were synthesized and oxidized by OH in environmental chambers under high- and low-NO conditions. We find that IEPOX reacts with OH at 299 K with rate coefficients of (0.84 ± 0.07) × 10(-11), (1.52 ± 0.07) × 10(-11), and (0.98 ± 0.05) × 10(-11) cm(3) molecule(-1) s(-1) for the ?1, cis-?, and trans-? isomers. Finally, yields of the first-generation products of IEPOX + OH oxidation were measured, and a new mechanism of IEPOX oxidation is proposed here to account for the observed products. The substantial yield of glyoxal and methylglyoxal from IEPOX oxidation may help explain elevated levels of those compounds observed in low-NO environments with high isoprene emissions. PMID:24476509

Bates, Kelvin H; Crounse, John D; St Clair, Jason M; Bennett, Nathan B; Nguyen, Tran B; Seinfeld, John H; Stoltz, Brian M; Wennberg, Paul O

2014-02-20

272

Volumes of Individual Amino Acid Residues in Gas-Phase Peptide Ions  

E-print Network

Volumes of Individual Amino Acid Residues in Gas-Phase Peptide Ions Anne E. Counterman and David E show that average volumes of individual Xxx residues in the gas phase are 5 to 15% smaller than when display preferential alignments.3 A key parameter in understanding packing is the volume that individual

Clemmer, David E.

273

Two-Phase Transport in Polymer Electrolyte Fuel Cells with Bilayer Cathode Gas Diffusion Media  

E-print Network

Two-Phase Transport in Polymer Electrolyte Fuel Cells with Bilayer Cathode Gas Diffusion Media Ugur to analyze the two-phase transport in polymer electrolyte fuel cells with bilayer cathode gas diffusion media toward the anode by increasing the hydraulic pressure differential across the membrane, consequently

274

Reactions in HostGuest Complexes Molecular Mousetraps: Gas-Phase Studies of the  

E-print Network

Reactions in Host­Guest Complexes Molecular Mousetraps: Gas-Phase Studies of the Covalent Coupling of purposes.[1,2] These noncovalent complexes are easily transferred to the gas phase by electrospray. May The Arnold and Mabel Beckman Laboratories of Chemical Syn- thesis, Division of Chemistry

Stoltz, Brian M.

275

Development and evaluation of the aerosol dynamic and gas phase chemistry model ADCHEM  

Microsoft Academic Search

The aim of this work was to develop a model ideally suited for detailed studies on aerosol dynamics, gas and particle phase chemistry within urban plumes, from local scale (1×1 km2) to regional or global scale. This article describes and evaluates the trajectory model for Aerosol Dynamics, gas and particle phase CHEMistry and radiative transfer (ADCHEM), which has been developed

P. Roldin; E. Swietlicki; G. Schurgers; A. Arneth; K. E. J. Lehtinen; M. Boy; M. Kulmala

2010-01-01

276

Development and evaluation of the aerosol dynamics and gas phase chemistry model ADCHEM  

Microsoft Academic Search

The aim of this work was to develop a model suited for detailed studies of aerosol dynamics, gas and particle phase chemistry within urban plumes, from local scale (1 × 1 km2) to regional scale. This article describes and evaluates the trajectory model for Aerosol Dynamics, gas and particle phase CHEMistry and radiative transfer (ADCHEM). The model treats both vertical

P. Roldin; E. Swietlicki; G. Schurgers; A. Arneth; K. E. J. Lehtinen; M. Boy; M. Kulmala

2011-01-01

277

ccsd-00001067(version2):11Mar2004 Nuclear liquid-gas phase transition and  

E-print Network

ccsd-00001067(version2):11Mar2004 Nuclear liquid-gas phase transition and supernovae evolution J appearing at the onset of the first order nuclear liquid-gas phase transition can play an important role of matter near the proto-neutron star surface. The resulting increase of pressure may induce strong particle

Boyer, Edmond

278

Steam generators two phase flows numerical simulation with liquid and gas momentum equations  

E-print Network

Steam generators two phase flows numerical simulation with liquid and gas momentum equations M Abstract This work takes place in steam generators flow studies and we consider here steady state three dimensional two-phase (liquid and gas) flows. The main goal is to improve the mod- eling of kinetic imbalance

Paris-Sud XI, Université de

279

DEMONSTRATION OF FUEL CELLS TO RECOVER ENERGY FROM LANDFILL GAS: PHASE II. PRETREATMENT SYSTEM PERFORMANCE MEASUREMENT  

EPA Science Inventory

The report describes Phase II of a demonstration of the utilization of commercial phosphoric acid fuel cells to recover energy from landfill gas. This phase consisted primarily of the construction and testing of a Gas Pretreatment Unit (GPU) whose function is to remove those impu...

280

DEMONSTRATION OF FUEL CELLS TO RECOVER ENERGY FROM LANDFILL GAS: PHASE II. PRETREATMENT SYSTEM PERFORMANCE MEASUREMENT  

EPA Science Inventory

The report describes-Phase II of a demonstration of the utilization of commercial phosphoric acid fuel cells to recover energy from landfill gas. his phase consisted primarily of the construction and testing of a Gas Pretreatment Unit (GPU) whose function is to remove those impur...

281

Nuclear symmetry energy effects on liquid-gas phase transition in hot asymmetric nuclear matter  

E-print Network

The liquid-gas phase transition in hot asymmetric nuclear matter is investigated within relativistic mean-field model using the density dependence of nuclear symmetry energy constrained from the measured neutron skin thickness of finite nuclei. We find symmetry energy has a significant influence on several features of liquid-gas phase transition. The boundary and area of the liquid-gas coexistence region, the maximal isospin asymmetry and the critical values of pressure and isospin asymmetry all of which systematically increase with increasing softness in the density dependence of symmetry energy. The critical temperature below which the liquid-gas mixed phase exists is found higher for a softer symmetry energy.

Bharat K. Sharma; Subrata Pal

2010-01-14

282

Sulfur doping of diamond films: Spectroscopic, electronic, and gas-phase studies  

E-print Network

by a model of the important gas phase chemical reactions, which recognizes the very different gas temperature diamond grown by chemical vapor deposition CVD have led to interest in such films for use in electronic-containing gases such as diborane to the standard CVD gas mixture 1% CH4 /H2 .3 Such films find use in UV detectors

Bristol, University of

283

Universal correlations of onedimensional interacting electrons in the gas phase F. Gohmann and V. E. Korepin  

E-print Network

Universal correlations of one­dimensional interacting electrons in the gas phase F. G¨ohmann and V electrons in one dimension at finite temperature. Below a critical value of the chemical potential temperature thermodynamics is that of an ideal gas. We identify the impenetrable electron gas model

284

Cluster Phase Chemistry: Gas-Phase Reactions of Anionic Sodium Salts of Dicarboxylic Acid Clusters with Water Molecules  

E-print Network

Cluster Phase Chemistry: Gas-Phase Reactions of Anionic Sodium Salts of Dicarboxylic Acid Clusters with Water Molecules Hugh I. Kim, William A. Goddard III,§ and J. L. Beauchamp*, Noyes Laboratory of Chemical of the activated cluster with water molecules. For example, with water addition, malonate clusters dissociate

Goddard III, William A.

285

Breakdown of a Topological Phase: Quantum Phase Transition in a Loop Gas Model with Tension Simon Trebst,1  

E-print Network

state. The transition can be understood as the condensation of ``magnetic'' vortices, leadingBreakdown of a Topological Phase: Quantum Phase Transition in a Loop Gas Model with Tension Simon the stability of topological order against local perturbations by considering the effect of a magnetic field

Trebst, Simon

286

Microfabricated gas chromatograph for rapid, trace-level determinations of gas-phase explosive marker compounds.  

PubMed

A prototype microfabricated gas chromatograph (?GC) adapted specifically for the rapid determination of selected gas-phase marker compounds of the explosive 2,4,6-trinitrotoluene (TNT) at sub-parts-per-billion (

Collin, William R; Serrano, Gustavo; Wright, Lindsay K; Chang, Hungwei; Nuñovero, Nicolás; Zellers, Edward T

2014-01-01

287

Homogeneous crystal nucleation in binary metallic melts  

NASA Technical Reports Server (NTRS)

A method for calculating the homogeneous crystal nucleation frequency in binary metallic melts is developed. The free energy of crystallization is derived from regular solution models for the liquid and solid and is used, together with model-based estimates of the interfacial tension, to calculate the nucleation frequency from the classical theory. The method can account for the composition dependence of the maximum undercooling observed in a number of experiments on small droplet dispersions. It can also be used to calculate the driving force for crystal growth and to obtain more precise estimates of the homogeneous crystal nucleation frequency in glass-forming alloys. This method, although approximate, is simple to apply, and requires only knowledge of the phase diagram and a few readily available thermodynamic quantities as input data.

Thompson, C. V.; Spaepen, F.

1983-01-01

288

Nucleation and growth of cracks in vitreous-bonded aluminum oxide at elevated temperatures  

Microsoft Academic Search

The nucleation and growth of cracks was studied at elevated temperatures on a grade of vitreous-bonded aluminium oxide that contained approx. =8 vol% glass at the grain boundaries. Cracks were observed to nucleate within the vitreous phase, close to the tensile surface of the flexural test specimens used in these experiments. Crack nucleation occurred at a strain of approx. =0.08%

K. Jakus; S. M. Wiederhorn; B. J. Hockey

1986-01-01

289

Crystal nucleation and cluster-growth kinetics in a model glass under shear  

E-print Network

Crystal nucleation and cluster-growth kinetics in a model glass under shear Anatolii V. Mokshin1, 2010) Crystal nucleation and growth processes induced by an externally applied shear strain in a model The study of phase transformation between liquid and crystal through a nucleation and subsequent growth

Paris-Sud XI, Université de

290

A comparison of heterogeneous ice nucleation parameterizations using a parcel model framework  

Microsoft Academic Search

A liquid-phase Lagrangian parcel model was expanded to include nucleation and growth of ice crystals. Intercomparisons between three heterogeneous ice nucleation parameterizations that link aerosol type and number to ice crystal concentration were conducted. Results indicate large differences in the prediction of ice formation in modestly supercooled clouds and in the susceptibility of cirrus to heterogeneous ice nucleation for the

Trude Eidhammer; Paul J. DeMott; Sonia M. Kreidenweis

2009-01-01

291

IV-VI semiconductor lasers for gas phase biomarker detection  

NASA Astrophysics Data System (ADS)

A promising absorption spectroscopy application for mid-IR lasers is exhaled breath analysis where sensitive, selective, and speedy measurement of small gas phase biomarker molecules can be used to diagnose disease and monitor therapies. Many molecules such as nitric oxide, ethane, formaldehyde, acetaldehyde, acetone, carbonyl sulfide, and carbon disulfide have been connected to diseases or conditions such as asthma, oxidative stress, breast cancer, lung cancer, diabetes, organ transplant rejection, and schizophrenia. Measuring these and other, yet to be discovered, biomarker molecules in exhaled breath with mid-IR lasers offers great potential for improving health care since such tests are non-invasive, real-time, and do not require expensive consumables or chemical reagents. Motivated by these potential benefits, mid-IR laser spectrometers equipped with presently available cryogenically-cooled IV-VI lasers mounted in compact Stirling coolers have been developed for clinical research applications. This paper will begin with a description of the development of mid-IR laser instruments and their use in the largest known exhaled breath clinical study ever performed. It will then shift to a description of recent work on the development of new IV-VI semiconductor quantum well materials and laser fabrication methods that offer the promise of low power consumption (i.e. efficient) continuous wave emission at room temperature. Taken together, the demonstration of compelling clinical applications with large market opportunities and the clear identification of a viable pathway to develop low cost mid-IR laser instrumentation can create a renewed focus for future research and development efforts within the mid-IR materials and devices area.

McCann, Patrick; Namjou, Khosrow; Roller, Chad; McMillen, Gina; Kamat, Pratyuma

2007-09-01

292

Laboratory Investigations of Titan Haze Formation: Characterization of Gas Phase and Particle Phase Nitrogen  

NASA Astrophysics Data System (ADS)

Prior to the arrival of the Cassini-Huygens spacecraft, aerosol production in Titan’s atmosphere was believed to begin in the stratosphere where chemical processes are predominantly initiated by far ultraviolet (FUV) radiation. However, the discovery of very heavy ions, coupled with Cassini Ultraviolet Imaging Spectrograph (UVIS) occultation measurements that show haze absorption up to 1000 km altitude (Liang et al., 2007), indicates that haze formation initiates in the thermosphere. The energy environment of the thermosphere is significantly different from the stratosphere; in particular there is a greater flux of extreme ultraviolet (EUV) photons and energetic particles available to initiate chemical reactions, including the destruction of N2, in the upper atmosphere. The discovery of previously unpredicted nitrogen species in measurements of Titan’s atmosphere by the Cassini Ion and Neutral Mass Spectrometer (INMS) indicates that nitrogen participates in the chemistry to a much greater extent than was appreciated before Cassini (Vuitton et al., 2007). Additionally, measurements obtained by the Aerosol Collector Pyrolyzer (ACP) carried by Huygens to Titan’s surface may indicate that Titan’s aerosols contain significant amounts of nitrogen (Israël et al., 2005, 2006). The degree of nitrogen incorporation in the haze particles is important for understanding the diversity of molecules that may be present in Titan’s atmosphere and on its surface. We have conducted a series of Titan atmosphere simulation experiments using either spark discharge (tesla coil) or FUV photons (deuterium lamp) to initiate chemistry in CH4/N2 gas mixtures ranging from 0.01% CH4/99.99% N2 to 10% CH4/90% N2. We obtained in situ measurements using a high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS) to measure the particle composition as a function of particle size and a proton-transfer ion-trap mass spectrometer (PIT-MS) to measure the composition of gas phase products. These two techniques allow us to investigate the effect of energy source and initial CH4 concentration on the degree of nitrogen incorporation in both the gas and solid phase products.

Horst, Sarah; Yoon, Heidi; Li, Rui; deGouw, Joost; Tolbert, Margaret

2014-11-01

293

Microgravity nucleation and particle coagulation experiments support  

NASA Technical Reports Server (NTRS)

A hollow sphere model is developed to predict the range of supersaturation ratio values for refractory metal vapors in a proposed experimental nucleation apparatus. Since the experiments are to be carried out in a microgravity environment, the model neglects the effects of convection and assumes that the only transfer of vapors through an inert gas atmosphere is by conduction and molecular diffusion. A consistent set of physical properties data is assembled for the various candidate metals and inert ambient gases expected to be used in the nucleation experiments. Transient partial pressure profiles are computed for the diffusing refractory species for two possible temperature distributions. The supersaturation ratio values from both candidate temperature profiles are compared with previously obtained experimetnal data on a silver-hydrogen system. The model is used to simulate the diffusion of magnesium vapor through argon and other inert gas atmospheres over ranges of initial and boundary conditions. These results identify different combinations of design and operating parameters which are liekly to produce supersaturation ratio values high enough to induce homogeneous nucleation in the apparatus being designed for the microgravity nucleation experiments.

Lilleleht, L. U.; Lass, T. J.

1987-01-01

294

Capillary effects on gas hydrate three-phase stability in marine sediments  

NASA Astrophysics Data System (ADS)

We study the three-phase (Liquid + Gas + Hydrate) stability of the methane hydrate system in marine sediments by considering the capillary effects on both hydrate and free gas phases. The aqueous CH4 solubilities required for forming hydrate (L+H) and free gas (L+G) in different pore sizes can be met in a three-phase zone. The top of the three-phase zone shifts upward in sediments as the water depth increases and the mean pore size decreases. The thickness of the three-phase zone increases as the pore size distribution widens. The top of the three-phase zone can either overlie the three-phase stability depth at deepwater Blake Ridge or underlie the three-phase stability depth at Hydrate Ridge in shallow water. Our model prediction is compatible with worldwide observations that the bottom-simulating reflector is systematically shifted upward relative to the bulk equilibrium depth as water depth (pressure) is increased. The gas hydrate and free gas saturations of the three-phase zone at Blake Ridge Comparison of the globally compiled BSR temperatures with the three-phase equilibrium curves for the systems of pure CH4 + 3.5 wt.% seawater (solid line) and pure CH4 + 2.0 wt.% seawater (dotted line). The discrepancies between the observed BSR temperature and the calculated three-phase temperature are systematically larger in deep water than in shallow water.

Liu, X.; Flemings, P. B.

2013-12-01

295

CO2 Capture from Flue Gas by Phase Transitional Absorption  

SciTech Connect

A novel absorption process called Phase Transitional Absorption was invented. What is the Phase Transitional Absorption? Phase Transitional Absorption is a two or multi phase absorption system, CO{sub 2} rich phase and CO{sub 2} lean phase. During Absorption, CO{sub 2} is accumulated in CO{sub 2} rich phase. After separating the two phases, CO{sub 2} rich phase is forward to regeneration. After regeneration, the regenerated CO{sub 2} rich phase combines CO{sub 2} lean phase to form absorbent again to complete the cycle. The advantage for Phase Transitional Absorption is obvious, significantly saving on regeneration energy. Because CO{sub 2} lean phase was separated before regeneration, only CO{sub 2} rich phase was forward to regeneration. The absorption system we developed has the features of high absorption rate, high loading and working capacity, low corrosion, low regeneration heat, no toxic to environment, etc. The process evaluation shows that our process is able to save 80% energy cost by comparing with MEA process.

Liang Hu

2009-06-30

296

Chlorine atom concentration determination via gas phase titration  

NASA Astrophysics Data System (ADS)

Chlorine oxidizes elemental mercury in coal flue gas. Addition of chlorine gas into an electrostatic precipitator, used to clean the flue gas, will thus increase the mercury removal efficiency in the precipitator. Determination of the chlorine atom concentration, formed inside the chamber, is a key to evaluate this efficiency. A series of experiments are performed to dissociate the chlorine gas in a corona-discharge field formed inside a 15X3 cm flow pyrex tube at P=1atm, and the chlorine atoms formed are measured by reacting them with butane. The reaction products are quantified using a GC-FID. The quantification of the chlorine atoms formed under varying parametric conditions like the voltage supplied, amount of chlorine gas injected into the reaction chamber and the distance between the electrodes will thus help in optimizing the amount of chlorine reagent gas needed to be added to a precipitator to obtain enhanced mercury removal efficiency.

Basu, Sreerupa

2006-10-01

297

Gas-phase production of single-walled carbon nanotubes from carbon monoxide: a review of the hipco process  

NASA Technical Reports Server (NTRS)

The latest process for producing large quantities of single-walled carbon nanotubes (SWNTs) to emerge from the Rice University, dubbed HiPco, is living up to its promise. The current production rates approach 450 mg/h (or 10 g/day), and nanotubes typically have no more than 7 mol % of iron impurities. Second-generation HiPco apparatus can run continuously for 7-10 days at a time. In the HiPco process nanotubes grow in high-pressure, high-temperature flowing CO on catalytic clusters of iron. Catalyst is formed in situ by thermal decomposition of iron pentacarbonyl, which is delivered intact within a cold CO flow and then rapidly mixed with hot CO in the reaction zone. Upon heating, the Fe(CO)5 decomposes into atoms that condense into larger clusters. SWNTs nucleate and grow on these particles in the gas phase via CO disproportionation: CO + CO --> CO2 + C (SWNT), catalyzed by the Fe surface. The concentration of CO2 produced in this reaction is equal to that of carbon and can therefore serve as a useful real-time feedback parameter. It was used to study and optimize SWNT production as a function of temperature, pressure, and Fe(CO)5 concentration. The results of the parametric study are in agreement with current understanding of the nanotube formation mechanism.

Nikolaev, Pavel

2004-01-01

298

Gas-phase production of single-walled carbon nanotubes from carbon monoxide: a review of the hipco process.  

PubMed

The latest process for producing large quantities of single-walled carbon nanotubes (SWNTs) to emerge from the Rice University, dubbed HiPco, is living up to its promise. The current production rates approach 450 mg/h (or 10 g/day), and nanotubes typically have no more than 7 mol % of iron impurities. Second-generation HiPco apparatus can run continuously for 7-10 days at a time. In the HiPco process nanotubes grow in high-pressure, high-temperature flowing CO on catalytic clusters of iron. Catalyst is formed in situ by thermal decomposition of iron pentacarbonyl, which is delivered intact within a cold CO flow and then rapidly mixed with hot CO in the reaction zone. Upon heating, the Fe(CO)5 decomposes into atoms that condense into larger clusters. SWNTs nucleate and grow on these particles in the gas phase via CO disproportionation: CO + CO --> CO2 + C (SWNT), catalyzed by the Fe surface. The concentration of CO2 produced in this reaction is equal to that of carbon and can therefore serve as a useful real-time feedback parameter. It was used to study and optimize SWNT production as a function of temperature, pressure, and Fe(CO)5 concentration. The results of the parametric study are in agreement with current understanding of the nanotube formation mechanism. PMID:15296221

Nikolaev, Pavel

2004-04-01

299

arXiv:0904.3065v1[cond-mat.quant-gas]20Apr2009 Symmetry breaking in quantum systems: the case study of vortex nucleation  

E-print Network

is the case of a fast rotating gas, when the number of vortices exceeds the number of particles. The GSarXiv:0904.3065v1[cond-mat.quant-gas]20Apr2009 Symmetry breaking in quantum systems: the case study field theory go back to the "molecular field theory" of Curie-Weiss [1] and concern magnetic phenomena

Dalibard, Jean

300

Single and Multicomponent Gas Phase Diffusion in a Porous Media: Modeling and Laboratory Measurements  

Microsoft Academic Search

Subsurface vapor migration of volatile chemicals may impact ambient and indoor air quality, increasing the importance to investigate the fate and transport of these chemicals. This project involved both modeling and experimental work to study the vapor phase transport behavior of single, binary, and tertiary component systems present in the gas phase. The experimental phase resulted in the development of

G. P. Partridge; Kevin S. McLeary; Tonia R. Showers; R. Scott Huebner; H. A. Elliott

2002-01-01

301

Two-phase gas bubble-liquid boundary layer flow along vertical and inclined surfaces  

SciTech Connect

The behavior of a two-phase gas bubble-liquid boundary layer along vertical and inclined porous surfaces with uniform gas injection is investigated experimentally and analytically. Using argon gas and water as the working fluids, a photographical study of the two-phase boundary layer flow has been performed for various angles of inclination ranging from 45/sup 0/ to 135/sup 0/ and gas injection rates ranging from 0.01 to 0.1 m/s. An integral method has been employed to solve the system of equations governing the two-phase motion. The effects of the gas injection rate and the angle of inclination on the growth of the boundary layer have been determined. The predicted boundary layer thickness is found to be in good agreement with the experimental results. The calculated axial liquid velocity and the void fraction in the two-phase region are also presented along with the observed flow behavior.

Cheung, F.B.; Epstein, M.

1985-01-01

302

[Characteristics of water-gas two-phase CO2 transport in unsaturated zone].  

PubMed

The migration of CO2 in soil was simulated through use of soil column, especially the transformation of CO2 between water and gas phases at wetting front was studied. The soil column in the test was 1 m long and the concentration of CO2 solution was 748 mg/L. Through analysis, it was shown that CO2 migration in water phase was governed by advection, dispersion, reaction and mass transfer between water and gas phases, that in gas phase by advection, dispersion, mass transfer between two phases. Sampling method under dynamic condition of two phase flow in soil column was approached and mass transfer coefficient from water phase to gas phase was determined as 0.00061. This showed that there was certain mass transformation of CO2 from water phase to gas phase and yet it was not so significant. This study can provide the quantitative scientific bases for safety assessment of geological disposal of low and intermediate level radioactive waste and environmental impact assessment of solid waste disposal by landfilling. PMID:14551970

Yu, Yanxin; Chen, Jiajun; Wang, Jinsheng; Yun, Ying; Li, Shushen; Wang, Zhiming

2003-07-01

303

FLUE GAS DESULFURIZATION PILOT STUDY. PHASE II. APPLICABILITY STUDY  

EPA Science Inventory

The North Atlantic Treaty Organization Committee on the Challenges of Modern Society (NATO-CCMS) Flue Gas Desulfurization (FGD) Study Group prepared status reports on 12 FGD processes. Results of this work are summarized in NATO Report No. 95 titled 'Flue Gas Desulfurization Pilo...

304

Gas phase dispersion in compost as a function of different water contents and air flow rates  

NASA Astrophysics Data System (ADS)

Gas phase dispersion in a natural porous medium (yard waste compost) was investigated as a function of gas flow velocity and compost volumetric water content using oxygen and nitrogen as tracer gases. The compost was chosen because it has a very wide water content range and because it represents a wide range of porous media, including soils and biofilter media. Column breakthrough curves for oxygen and nitrogen were measured at relatively low pore gas velocities, corresponding to those observed in for instance soil vapor extraction systems or biofilters for air cleaning at biogas plants or composting facilities. Total gas mechanical dispersion-molecular diffusion coefficients were fitted from the breakthrough curves using a one-dimensional numerical solution to the advection-dispersion equation and used to determine gas dispersivities at different volumetric gas contents. The results showed that gas mechanical dispersion dominated over molecular diffusion with mechanical dispersion for all water contents and pore gas velocities investigated. Importance of mechanical dispersion increased with increasing pore gas velocity and compost water content. The results further showed that gas dispersivity was relatively constant at high values of compost gas-filled porosity but increased with decreasing gas-filled porosity at lower values of gas-filled porosity. Results finally showed that measurement uncertainty in gas dispersivity is generally highest at low values of pore gas velocity.

Sharma, Prabhakar; Poulsen, Tjalfe G.

2009-07-01

305

A new approach in modelling phase equilibria and gas solubility in electrolyte solutions and its applications to gas hydrates  

Microsoft Academic Search

This paper presents a new predictive model for phase equilibria and gas solubility calculations in the presence of electrolyte solutions. It treats salts as pseudo-components in an equation of state (EoS) by defining the critical properties and acentric factor for each salt. The water–salt, gas–salt and salt–salt binary interaction parameters (BIP) have been determined by using available experimental data on

Rahim Masoudi; Bahman Tohidi; Ali Danesh; Adrian C. Todd

2004-01-01

306

The gas-phase metallicity of central and satellite galaxies in the Sloan Digital Sky Survey  

NASA Astrophysics Data System (ADS)

We exploit the galaxy groups catalogue of Yang et al. and the galaxy properties measured in the Sloan Digital Sky Survey Data Releases 4 and 7 to study how the gas-phase metallicities of star-forming galaxies depend on environment. We find that satellite and central galaxies follow a qualitatively similar stellar mass (M?)-gas-phase metallicity relation, whereby their gas-phase metallicity increases with M?. Satellites, though, have higher gas-phase metallicities than equally massive centrals, and this difference increases with decreasing stellar mass. We find a maximum offset of 0.06 dex at log(M?/h-2 M?) ? 8.25. At fixed halo mass, centrals are more metal rich than satellites by ˜0.5 dex on average. This is simply due to the fact that, by definition, centrals are the most massive galaxies in their groups, and the fact that gas-phase metallicity increases with stellar mass. More interestingly, we also find that the gas-phase metallicity of satellites increases with halo mass (Mh) at fixed stellar mass. This increment is more pronounced for less massive galaxies, and, at M? ? 109 h-2 M?, corresponds to ˜0.15 dex across the range 11 < log (Mh/h-1 M?) < 14. We also show that low-mass satellite galaxies have higher gas-phase metallicities than central galaxies of the same stellar metallicity. This difference becomes negligible for more massive galaxies of roughly solar metallicity. We demonstrate that the observed differences in gas-phase metallicity between centrals and satellites at fixed M? are not a consequence of stellar mass stripping (advocated by Pasquali et al. in order to explain similar differences but in stellar metallicity), nor to the past star formation history of these galaxies as quantified by their surface mass density or gas mass fraction. Rather, we argue that these trends probably originate from a combination of three environmental effects: (i) strangulation, which prevents satellite galaxies from accreting new, low-metallicity gas which would otherwise dilute their interstellar medium; (ii) ram pressure stripping of the outer gas disc, thereby inhibiting radial inflows of low-metallicity gas and (iii) external pressure provided by the hot gas of the host halo which prevents metal-enriched outflows from escaping the galaxies. Each of these three mechanisms naturally explains why the difference in gas-phase metallicity between centrals and satellites increases with decreasing stellar mass and with increasing host halo mass, at least qualitatively. However, more detailed simulations and observations are required in order to discriminate between these mechanisms, and to test, in detail, whether they are consistent with the data.

Pasquali, Anna; Gallazzi, Anna; van den Bosch, Frank C.

2012-09-01

307

An investigation into the flow behavior of a single phase gas system and a two phase gas/liquid system in normal gravity with nonuniform heating from above  

NASA Technical Reports Server (NTRS)

The fluid behavior in normal gravity of a single phase gas system and a two phase gas/liquid system in an enclosed circular cylinder heated suddenly and nonuniformly from above was investigated. Flow visualization was used to obtain qualitative data on both systems. The use of thermochromatic liquid crystal particles as liquid phase flow tracers was evaluated as a possible means of simultaneously gathering both flow pattern and temperature gradient data for the two phase system. The results of the flow visualization experiments performed on both systems can be used to gain a better understanding of the behavior of such systems in a reduced gravity environment and aid in the verification of a numerical model of the system.

Disimile, Peter J.; Heist, Timothy J.

1990-01-01

308

Gas phase antimony\\/tungsten\\/oxygen cluster cations  

Microsoft Academic Search

Sb\\/W\\/O cluster ions were produced using a gas-aggregation source and were investigated by time-of-flight mass spectrometry following ionization with a 266-nm YAG laser. A W-heater in the presence of O2 gas and Sb vapor reacted to produce the Sb\\/W\\/O species, followed by ionization and fragmentation to produce stable cluster ions which could be observed in mass spectra. Two series of

Tsunehiko Fujiwara; Akiko Iizuka; Koken Sato; Yasuhiro Yamada

2005-01-01

309

Gas phase reaction products during tungsten atomic layer deposition using WF6 and Si2H6  

E-print Network

Gas phase reaction products during tungsten atomic layer deposition using WF6 and Si2H6 R. K; published 23 July 2004 The gas phase reaction products during tungsten W atomic layer deposition ALD using WF6 and Si2H6 were studied using quadrupole mass spectrometry. The gas phase reactions products were

George, Steven M.

310

Modeling of Two-Phase Behavior in the Gas Diffusion Medium of PEFCs via Full Morphology Approach  

E-print Network

-phase characteristics of the gas diffusion medium in a polymer electrolyte fuel cell PEFC . The three-dimensional 3D two-phase models. Additionally, 3D visualization of the water distribution in the gas diffusion mediumModeling of Two-Phase Behavior in the Gas Diffusion Medium of PEFCs via Full Morphology Approach

311

Source apportionment of wintertime gas-phase and particle-phase air pollutants using organic compounds as tracers  

SciTech Connect

Two chemical mass balance receptor models are developed which can determine the source contributions to atmospheric pollutant concentrations using organic compounds as tracers. The first model uses particle-phase organic compounds to apportion the primary source contribution to atmospheric fine particulate organic carbon concentrations and fine particle mass concentrations. The second receptor model simultaneously uses both volatile gas-phase hydrocarbon and particle-phase organic compounds as tracers to determine source contributions to non-methane organic gases in the atmosphere. Both models are applied to data collected in California's San Joaquin Valley during two severe wintertime air pollution episodes. Source contributions to fine particle air quality are calculated for two urban sites, Fresno and Bakersfield, and one background site, Kern Wildlife Refuge. Primary particle emissions from hardwood combustion, softwood combustion, diesel engines, meat cooking, and gasoline-powered motor vehicles contribute on average 79% of the airborne fine particle organic compound mass at the urban sites during both episodes with smaller but still measurable contributions from fine particle road dust and natural gas combustion aerosol. Anthropogenic primary particle sources contribute less than 10% of the fine particle mass concentration at the background site. The combined gas-phase and particle-phase organic compound receptor model shows that gasoline-powered motor vehicle exhaust and gasoline vapors are the largest contributors to nonmethane organic gases concentrations followed by natural gas leakage. Smaller but statistically significant contributions to organic vapors from wood combustion, meat cooking, and diesel exhaust also are quantified.

Schauer, J.J.; Cass, G.R.

2000-05-01

312

Gas-phase mercury reduction to measure total mercury in the flue gas of a coal-fired boiler.  

PubMed

Gaseous elemental and total (elemental + oxidized) mercury (Hg) in the flue gas from a coal-fired boiler was measured by a modified ultraviolet (UV) spectrometer. Challenges to Hg measurement were the spectral interferences from other flue gas components and that UV measures only elemental Hg. To eliminate interference from flue gas components, a cartridge filled with gold-coated sand removed elemental Hg from a flue gas sample. The Hg-free flue gas was the reference gas, eliminating the spectral interferences. To measure total Hg by UV, oxidized Hg underwent a gas-phase, thermal-reduction in a quartz cell heated to 750 degrees C. Simultaneously, hydrogen was added to flash react with the oxygen present forming water vapor and preventing Hg re-oxidation as it exits the cell. Hg concentration results are in parts per billion by volume Hg at the flue gas oxygen concentration. The modified Hg analyzer and the Ontario Hydro method concurrently measured Hg at a field test site. Measurements were made at a 700-MW steam turbine plant with scrubber units and selective catalytic reduction. The flue gas sampled downstream of the selective catalytic reduction contained 2100 ppm SO2 and 75 ppm NOx. Total Hg measured by the Hg analyzer was within 20% of the Ontario Hydro results. PMID:14871013

Meischen, Sandra J; Van Pelt, Vincent J; Zarate, Eugene A; Stephens, Edward A

2004-01-01

313

Comparing gas-phase and grain-catalyzed H2 formation  

E-print Network

Because H2 formation on dust grain surfaces completely dominates gas-phase H2 formation in local molecular clouds, it is often assumed that gas-phase formation is never important. In fact, it is the dominant mechanism in a number of cases. In this paper, I briefly summarize the chemistry of gas-phase H2 formation, and show that it dominates for dust-to-gas ratios less than a critical value D_cr. I also show that D_cr is simple to calculate for any given astrophysical situation, and illustrate this with a number of examples, ranging from H2 formation in warm atomic gas in the Milky Way to the formation of protogalaxies at high redshift.

Simon C. O. Glover

2002-10-22

314

FACTORS INFLUENCING THE DEPOSITION OF A COMPOUND THAT PARTITIONS BETWEEN GAS AND PARTICULATE PHASES  

EPA Science Inventory

How will atmospheric deposition behave for a compound when it reversibly sorbs between gas and atmospheric particulate phases? Two factors influence the answer. What physical mechanisms occur in the sorption process? What are the concentration and composition of atmospheric par...

315

Determination of Gas-Phase Dimethyl Sulfate and Monomethyl Hydrogen Sulfate.  

National Technical Information Service (NTIS)

Analytical techniques have been developed for the collection and determination of gas phase dimethyl sulfate and monomethyl sulfuric acid in the flue lines and plumes of power plants and in the ambient atmosphere. The techniques involve the collection of ...

L. D. Hansen, V. F. White, D. J. Eatough

1986-01-01

316

Numerical Simulation of Bubble Merger Process on a Single Nucleation Site During Pool Nucleate Boiling  

Microsoft Academic Search

A bubble merger process on a single nucleation site has been investigated by numerically solving the equations governing conservation of mass, momentum and energy in the vapor and liquid phases. The vapor-liquid interface is captured by a level set method which can easily handle breaking and merging of the interface. The level set method is modified to include the effects

N. Ramanujapu; V. K. Dhir

2002-01-01

317

Modeling nongray gas-phase and soot radiation in luminous turbulent nonpremixed jet flames  

Microsoft Academic Search

Much progress has been made in radiative heat transfer modeling with respect to treatment of nongray radiation from both gas-phase species and soot particles, while radiation modeling in turbulent flame simulations is still in its infancy. Aiming at reducing this gap, this paper introduces state-of-the-art models of gas-phase and soot radiation to turbulent flame simulations. The full-spectrum k-distribution method (Modest,

L. Wang; M. F. Modest; D. C. Haworth; S. R. Turns

2005-01-01

318

Scaling analysis of gas-liquid two-phase flow pattern in microgravity  

NASA Technical Reports Server (NTRS)

A scaling analysis of gas-liquid two-phase flow pattern in microgravity, based on the dominant physical mechanism, was carried out with the goal of predicting the gas-liquid two-phase flow regime in a pipe under conditions of microgravity. The results demonstrated the effect of inlet geometry on the flow regime transition. A comparison of the predictions with existing experimental data showed good agreement.

Lee, Jinho

1993-01-01

319

Gas-Phase Molecular Dynamics: High Resolution Spectroscopy and Collision Dynamics of Transient Species  

SciTech Connect

This research is carried out as part of the Gas-Phase Molecular Dynamics program in the Chemistry Department at Brookhaven National Laboratory. Chemical intermediates in the elementary gas-phase reactions involved in combustion chemistry are investigated by high resolution spectroscopic tools. Production, reaction, and energy transfer processes are investigated by transient, double resonance, polarization and saturation spectroscopies, with an emphasis on technique development and connection with theory, as well as specific molecular properties.

Hall, G.E.

2011-05-31

320

Purification of high conductive liquid using gas-liquid phases discharge reactor  

Microsoft Academic Search

Water purification by streamer discharge using pulsed power generator under the high conductivity water containing pollutants has been investigated. A gas-liquid separated reactor was developed to treat high conductive solution. A wire electrode was placed in the gas phase and a plane electrode was immersed in the water. The pulsed high voltage generated by six stacked Blumlein line was applied

K. Takahashi; Y. Sasaki; S. Mukaigawa; K. Takaki; T. Fujiwara; N. Satta

2009-01-01

321

Dynamics of particle growth and overheating in gas-phase polymerization reactors  

Microsoft Academic Search

The particle overheating is an important problem in the industrial catalytic gas-phase olefin polymerization reactors. It has been first investigated with a pseudo-stationary model of a single polymer particle by Hutchinson and Ray (J. Appl. Poly. Sci. 34 (1987) 657). A systematic study of overheating of polymer particle with models based on Fick's and dusty gas model (DGM) transport described

J. Kosek; Z. Grof; A. ák; F. Št?pánek; M. Marek

2001-01-01

322

Modeling the phase partitioning behavior of gas tracers under geothermal reservoir conditions  

Microsoft Academic Search

A model of the liquid-vapor phase partitioning behavior of low concentrations of gas tracers in water at geothermal temperatures and pressures is presented. This model uses Henry's coefficient to describe the variation of the gas tracer solubility with temperature and pressure. A new method is described for the determination and representation of Henry's coefficients. The method uses experimentally determined values

Mark Trew; Michael J. O'Sullivan; Yoshio Yasuda

2001-01-01

323

Gas-phase boundary layer ignition on a catalytic flat plate with heat loss  

Microsoft Academic Search

The gas-phase ignition of a premixed boundary layer flow by a nonisothermal plate with very large catalytic efficiency is studied. The catalytic upper side of the plate is in contact with the premixed gas while the lower side is held at constant temperature. The catalytic reaction is assumed to be ignited and diffusion controlled. The temperature on this side changes

C. Trevino; N. Peters

1985-01-01

324

Intense Mechanoluminescence and Gas Phase Reactions from the Sonication of an Organic Slurry  

E-print Network

reported ML from sonication of slurries of piezoelectric organic crystals in long chain alkanes,5 and the NIntense Mechanoluminescence and Gas Phase Reactions from the Sonication of an Organic Slurry Nathan of mechanical stress to a crystal.1 This light is the result of a dielectric breakdown of the intervening gas

Suslick, Kenneth S.

325

Air purification in chemical and biological warfare environments using gas-phase corona reactor technology  

Microsoft Academic Search

Chemical and biological warfare materials create difficulties when designing or retrofitting high value targets such as buildings to withstand terrorist attack. The gas-phase corona reactor (GPCR) is a synergistic combination of plasma (or ionized gas) and catalyst technologies to produce an air purification system. The GPCR has demonstrated both chemical agent decomposition and biological material deactivation creating a universal air

Joseph G. Birmingham; Gautam Pillay

1997-01-01

326

Experimental and gas phase modeling of nanocrystalline diamond films grown on titanium alloys for biomedical applications  

Microsoft Academic Search

For biomedical applications, it is highly desirable to be able to deposit smooth adherent diamond films on various complex-shaped substrates using the hot filament chemical vapor deposition technique (HFCVD). The properties of these films are affected profoundly by process parameters such as filament temperature, gas composition, and pressure. In this study, we present an insight into the gas phase chemistry

M. J. Jackson; A. N. Jones; W. Ahmed

2005-01-01

327

APPLICATIONS ANALYSIS REPORT: ECO LOGIC INTERNATIONAL GAS-PHASE CHEMICAL REDUCTION PROCESS - THE REACTOR SYSTEM  

EPA Science Inventory

This report details the Superfund Innovative Technology Evaluation of Eco Logic International's gas-phase chemical reduction process, with an emphasis on their Reactor System. he Eco Logic process employees a high temperature reactor filled with hydrogen gas as the means to destr...

328

Prediction of methanol loss in vapor phase during gas hydrate inhibition using Arrhenius-type functions  

Microsoft Academic Search

Gas hydrate formation in natural gas and NGL systems can block pipelines, equipment, and instruments, restricting or interrupting flow leading to safety hazards to production\\/transportation systems and to substantial economic risks. The amount of hydrate inhibitor to be injected not only must be sufficient to prevent freezing of the inhibitor water phase, but also must be sufficient to provide for

Alireza Bahadori; Hari B. Vuthaluru

2010-01-01

329

Carbon Nanotube Stationary Phase in a Microfabricated Column for High-Performance Gas Chromatography  

E-print Network

Chromatography Takashi Nakai* , Jun Okawa, Shuji Takada, Masaki Shuzo* , Junichiro Shiomi, Jean-Jacques Delaunay a microfabricated gas chromatography (GC) column that uses a thin layer of high-quality single- walled carbon useful for high-performance micro-GC. Keywords: Carbon Nanotube, Stationary Phase, Gas Chromatography

Maruyama, Shigeo

330

Application of the gas phase condensation to the preparation of nanoparticles  

Microsoft Academic Search

The evaporation of materials in ultra-high vacuum leads to the growth of thin films on appropriated substrates. In the presence of an inert gas (pressure above 10?1Torr), the evaporated materials lose kinetic energy by collisions with the inert gas molecules in the gas phase and condense in the form of nanometric size crystallites that can be collected on the substrate

A. Fernández; E. P. Reddy; T. C. Rojas; J. C. Sánchez-López

1999-01-01

331

Phase transitions in a 3 dimensional lattice loop gas  

E-print Network

We investigate, via Monte Carlo simulations, the phase structure of a system of closed, nonintersecting but otherwise non-interacting, loops in 3 Euclidean dimensions. The loops correspond to closed trajectories of massive particles and we find a phase transition as a function of their mass. We identify the order parameter as the average length of the loops at equilibrium. This order parameter exhibits a sharp increase as the mass is decreased through a critical value, the behaviour seems to be a cross-over transition. We believe that the model represents an effective description of the broken-symmetry sector of the 2+1 dimensional abelian Higgs model, in the extreme strong coupling limit. The massive gauge bosons and the neutral scalars are decoupled, and the relevant low-lying excitations correspond to vortices and anti-vortices. The functional integral can be approximated by a sum over simple, closed vortex loop configurations. We present a novel fashion to generate non-intersecting closed loops, starting from a tetrahedral tessellation of three space. The two phases that we find admit the following interpretation: the usual Higgs phase and a novel phase which is heralded by the appearance of effectively infinitely long loops. We compute the expectation value of the Wilson loop operator and that of the Polyakov loop operator. The Wilson loop exhibits perimeter law behaviour in both phases implying that the transition corresponds neither to the restoration of symmetry nor to confinement. The effective interaction between external charges is screened in both phases, however there is a dramatic increase in the polarization cloud in the novel phase as shown by the energy shift introduced by the Wilson loop.

Richard MacKenzie; F. Nebia-Rahal; M. B. Paranjape

2007-10-17

332

Ceramic stationary gas turbine development. Final report, Phase 1  

SciTech Connect

This report summarizes work performed by Solar Turbines Inc. and its subcontractors during the period September 25, 1992 through April 30, 1993. The objective of the work is to improve the performance of stationary gas turbines in cogeneration through implementation of selected ceramic components.

NONE

1994-09-01

333

Haloalkane hydrolysis by Rhodococcus erythropolis cells: comparison of conventional aqueous phase dehalogenation and nonconventional gas phase dehalogenation.  

PubMed

Biofiltration of air polluted by volatile organic compounds is now recognized by the industrial and research communities as an effective and viable alternative to standard environmental technologies. Whereas many studies have focused on solid/liquid/gas biofilters, there have been fewer reports on waste air treatment using other biological processes, especially in a solid/gas biofilter. In this study, a comparison was made of the hydrolysis of halogenated compounds (such as 1-chlorobutane) by lyophilized Rhodococcus erythropolis cells in a novel solid/gas biofilter and in the aqueous phase. We first determined the culture conditions for the production of R. erythropolis cells with a strong dehalogenase activity. Four different media were studied and the amount of 1-chlorobutane was optimized. Next, we report the possibility to use R. erythropolis cells in a solid/gas biofilter in order to transform halogenated compounds in corresponding alcohols. The effect of experimental parameters (total flow into the biofilter, thermodynamic activity of the substrates, temperature, carbon chain length of halogenated substrates) on the activity and stability of lyophilized cells in the gas phase was determined. A critical water thermodynamic activity (a(w)) of 0.4 is necessary for the enzyme to become active and optimal dehalogenase activity for the lyophilized cells is obtained for an a(w) of 0.9. A temperature of reaction of 40 degrees C represents the best compromise between stability and activity. Activation energy of the reaction was determined and found equal to 59.5 KJ/mol. The pH effect on the dehalogenase activity of R. erythropolis cells was also studied in the gas phase and in the aqueous phase. It was observed that pH 9.0 provided the best activity in both systems. We observed that in the aqueous phase R. erythropolis cells were less sensitive to the variation in pH than R. erythropolis cells in the gas phase. Finally, the addition of volatile Lewis base (triethylamine) in the gaseous phase and the action of the lysozyme in order to permeabilize the cells was found to be highly beneficial to the effectiveness of the biofilter. PMID:15007840

Erable, Benjamin; Goubet, Isabelle; Lamare, Sylvain; Legoy, Marie Dominique; Maugard, Thierry

2004-04-01

334

Nucleation of the AB transition in superfluid 3He: Surface effects and baked Alaska  

NASA Astrophysics Data System (ADS)

The first-order phase transition between the A and B phases of superfluid 3He has remained an outstanding mystery in helium physics for nearly 20 years. The small difference in bulk free energies between the two phases, combined with the relatively large surface energy associated with the AB interface, leads to an anomalously large critical radius for nucleation, of order 1 ?m, suggesting a lifetime for the super-cooled A phase against homogeneous nucleation far beyond the age of the universe. Yet anisotropy of the high-temperature phase minimizes the depairing effects of surfaces, thus making conventional heterogeneous nucleation unlikely. Recent experiments have been reported that lend support to one of the more exotic nucleation mechanisms ever proposed: Leggett's "baked Alaska" model, in which the B phase is nucleated by cosmic rays penetrating the supercooled A phase. The results of these experiments are discussed, along with the prospects for future work.

Schiffer, P.; Osheroff, D. D.

1995-04-01

335

The Vaguries of Pyroxene Nucleation and the Resulting Chondrule Textures  

NASA Technical Reports Server (NTRS)

Pyroxene is a major phase in chondrules, but often follows olivine in the crystallization sequence and depending on the melting temperature and time may not nucleate readily upon cooling. Dynamic crystallization experiments based on total or near total melting were used to study PO (porphyritic olivine) and PP (Porphyritic pyroxene) compositions as defined by. The experiments showed that pyroxene nucleated only at subliquidus temperatures in the PP melts and rarely in the PO melts. Porphyritic chondrules with phenocrysts of both olivine and pyroxene (POP chondrules) were not easily produced in the experiments. POP chondrules are common and it is important for deciphering their formation that we understand pyroxene nucleation properties of chondrule melts.

Lofgren, G. E.; Le, L.

2004-01-01

336

Gas phase investigations of sulfonium salts by electrospray ft-icr/ms  

NASA Astrophysics Data System (ADS)

Twelve sulfonium salts were studied by electrospray Fourier transform ion cyclotron resonance mass spectrometry. Collisionally activated dissociation, CAD, reactions, using neutral argon as the collision gas, were performed to investigate dissociation pathways in the gas phase and to study the stabilizing/destabilizing effects of electron donating/withdrawing substituents on the sulfonium ions. Ion-molecule reactions were attempted to identify SN2 reaction mechanisms, but to date we have detected exclusively SN1-type reactions in the gas phase. Literature reports on the mass spectrometry of sulfonium cations are reviewed.

Katritzky, Alan R.; Shipkova, Petia A.; Watson, Clifford H.; Eyler, John R.; Kevill, Dennis N.

1997-11-01

337

Small gas-phase dianions produced by sputtering and gas flooding  

SciTech Connect

We have extended our previous experiment [Schauer et al., Phys. Rev. Lett. 65, 625 (1990)] where we had produced small gas-phase dianion clusters of C{sub n}{sup 2-}(n{>=}7) by means of sputtering a graphite surface by Cs{sup +} ion bombardment. Our detection sensitivity for small C{sub n}{sup 2-} could now be increased by a factor of about 50 for odd n. Nevertheless, a search for the elusive pentamer dianion of C{sub 5}{sup 2-} was not successful. As an upper limit, the sputtered flux of C{sub 5}{sup 2-} must be at least a factor of 5000 lower than that of C{sub 7}{sup 2-}, provided that the lifetime of C{sub 5}{sup 2-} is sufficiently long to allow its detection by mass spectrometry. When oxygen gas (flooding with either O{sub 2} or with N{sub 2}O) was supplied to the Cs{sup +}-bombarded graphite surface, small dianions of OC{sub n}{sup 2-}(5{<=}n{<=}14) and O{sub 2}C{sub 7}{sup 2-} were observed in addition to C{sub n}{sup 2-}(n{>=}7). Similarly, Cs{sup +} sputtering of graphite with simultaneous SF{sub 6} gas flooding produced SC{sub n}{sup 2-}(6{<=}n{<=}18). Mixed nitrogen-carbon or fluorine-carbon dianion clusters could not be observed by these means. Attempts to detect mixed metal-fluoride dianions for SF{sub 6} gas flooding of various Cs{sup +}-bombarded metal surfaces were successful for the case of Zr, where metastable ZrF{sub 6}{sup 2-} was observed. Cs{sup +} bombardment of a silicon carbide (SiC) wafer produced SiC{sub n}{sup 2-} (n=6,8,10). When oxygen gas was supplied to the Cs{sup +}-bombarded SiC surface, small dianions of SiOC{sub n}{sup 2-} (n=4,6,8) and of SiO{sub 2}C{sub n}{sup 2-} (n=4,6) as well as a heavier unidentified dianion (at m/z=98.5) were observed. For toluene (C{sub 7}H{sub 8}) vapor flooding of a Cs{sup +}-bombarded graphite surface, several hydrocarbon dianion clusters of C{sub n}H{sub m}{sup 2-}(n{>=}7) were produced in addition to C{sub n}{sup 2-}(n{>=}7), while smaller C{sub n}H{sub m}{sup 2-} with n{<=}6 could not be observed. BeC{sub n}{sup 2-} (n=4,6,8,10), Be{sub 2}C{sub 6}{sup 2-}, as well as BeC{sub 8}H{sub m}{sup 2-} (with m=2 and/or m=1) were observed for toluene vapor flooding of a Cs{sup +}-bombarded beryllium metal foil. The metastable pentamer {sup 9}Be{sup 12}C{sub 4}{sup 2-} at m/z=28.5 was the smallest and lightest dianion molecule that we could detect. The small dianion clusters of SC{sub n}{sup 2-}, OC{sub n}{sup 2-}, BeC{sub n}{sup 2-}, and SiO{sub m}C{sub n}{sup 2-} (m=0,1,2) have different abundance patterns. A resemblance exists between the abundance patterns of BeC{sub n}{sup 2-} and SiC{sub n}{sup 2-}, even though calculated molecular structures of BeC{sub 6}{sup 2-} and SiC{sub 6}{sup 2-} are different. The abundance pattern of SC{sub n}{sup 2-} is fairly similar to that of C{sub n}{sup 2-}.

Franzreb, Klaus; Williams, Peter [Department of Chemistry and Biochemistry, Arizona State University, Tempe, Arizona 85287 (United States)

2005-12-08

338

Computational Science Technical Note CSTN-132 Visualising Multi-Phase Lattice Gas Fluid Layering Simulations  

E-print Network

insights into the essential behaviours. We describe sim- ulations of multi-phase layering in a lattice gas still reveal good insights into the essential behaviours. We describe simulations of multi Introduction Complex fluids such as multi-phase systems of sand, mud, oil and so forth[1] have attracted

Hawick, Ken

339

Liquid-Gas Relative Permeabilities in Fractures: Effects of Flow Structures, Phase Transformation and Surface  

E-print Network

SGP-TR-177 Liquid-Gas Relative Permeabilities in Fractures: Effects of Flow Structures, Phase Rights Reserved #12;iv Abstract Two-phase flow through fractured media is important in petroleum fractures are poorly understood, and oversimplified relative permeability curves are commonly used

Stanford University

340

Structural properties of iron disilicide nanocrystals from the gas phase investigated by advanced electron microscopy  

E-print Network

) and iron pentacarbonyl (Fe(CO)5) in a hot wall reactor. The as-prepared material typically consistsStructural properties of iron disilicide nanocrystals from the gas phase investigated by advanced, planar defects, Stripe-STEM, Cc corrected EFTEM Beta-phase iron disilicide (-FeSi2) is a promising

Dunin-Borkowski, Rafal E.

341

ANALYSIS OF A GAS-PHASE PARTITIONING TRACER TEST CONDUCTED THROUGH FRACTURED MEDIA  

EPA Science Inventory

The gas-phase partitioning tracer method was used to estimate non-aqueous phase liquid (NAPL), water, and air saturations in the vadose zone at a chlorinated-solvent contaminated field site in Tucson, AZ. The tracer test was conducted in a fractured clay system that is the confin...

342

Separation of gas from liquid in a two-phase flow system  

NASA Technical Reports Server (NTRS)

Separation system causes jets which leave two-phase nozzles to impinge on each other, so that liquid from jets tends to coalesce in center of combined jet streams while gas phase is forced to outer periphery. Thus, because liquid coalescence is achieved without resort to separation with solid surfaces, cycle efficiency is improved.

Hayes, L. G.; Elliott, D. G.

1973-01-01

343

Polymer crystal-melt interfaces and nucleation in polyethylene  

E-print Network

Kinetic barriers cause polymers to crystallize incompletely, into nanoscale lamellae interleaved with amorphous regions. As a result, crystalline polymers are full of crystal-melt interfaces, which dominate their physical properties. The longstanding theoretical challenge to understand these interfaces has new relevance, because of accumulating evidence that polymer crystals often nucleate via a metastable, partially ordered "rotator" phase. To test this idea requires a theory of the bulk and interfacial free energies of the critical nucleus. We present a new approach to the crystal-melt interface, which represents the amorphous region as a grafted brush of loops in a self-consistent pressure field. We combine this theory with estimates of bulk free energy differences, to calculate nucleation barriers and rates via rotator versus crystal nuclei for polyethylene. We find rotator-phase nucleation is indeed favored throughout the temperature range where nucleation is observed. Our methods can be extended to other polymers.

Scott T. Milner

2010-09-22

344

Surface Nanobubbles Nucleate Microdroplets  

NASA Astrophysics Data System (ADS)

When a hydrophobic solid is in contact with water, surface nanobubbles often form at the interface. They have a lifetime many orders of magnitude longer than expected. Here, we show that they even withstand a temperature increase to temperatures close to the boiling point of bulk water; i.e., they do not nucleate larger bubbles ("superstability"). On the contrary, when the vapor-liquid contact line passes a nanobubble, a liquid film remains around it, which, after pinch-off, results in a microdroplet in which the nanobubbles continue to exist. Finally, the microdroplet evaporates and the nanobubble consequently bursts. Our results support that pinning plays a crucial role for nanobubble stability.

Zhang, Xuehua; Lhuissier, Henri; Sun, Chao; Lohse, Detlef

2014-04-01

345

Nucleation dynamics of water nanodroplets.  

PubMed

The origin of the condensation of water begins at the nanoscale, a length-scale that is challenging to probe for liquids. In this work we directly image heterogeneous nucleation of water nanodroplets by in situ transmission electron microscopy. Using gold nanoparticles bound to a flat surface as heterogeneous nucleation sites, we observe nucleation and growth of water nanodroplets. The growth of nanodroplet radii follows the power law: R(t)~(t-t 0) ? , where ?~0.2-0.3. PMID:24667092

Bhattacharya, Dipanjan; Bosman, Michel; Mokkapati, Venkata R S S; Leong, Fong Yew; Mirsaidov, Utkur

2014-04-01

346

Fragmentation and the Bose-glass phase transition of the disordered one-dimensional Bose gas  

SciTech Connect

We investigate the superfluid-insulator quantum phase transition in a disordered one-dimensional Bose gas in the mean-field limit by studying the probability distribution of the density. The superfluid phase is characterized by a vanishing probability to have zero density, whereas a nonzero probability marks the insulator phase. This relation is derived analytically and confirmed by a numerical study. This fragmentation criterion is particularly suited for detecting the phase transition in experiments. When a harmonic trap is included, the transition to the insulating phase can be extracted from the statistics of the local density distribution.

Fontanesi, Luca; Wouters, Michiel; Savona, Vincenzo [Institute of Theoretical Physics, Ecole Polytechnique Federale de Lausanne EPFL, CH-1015 Lausanne (Switzerland)

2011-03-15

347

Gas distribution equipment in hydrogen service - Phase II  

NASA Technical Reports Server (NTRS)

The hydrogen permeability of three different types of commercially available natural gas polyethylene pipes was determined. Ring tensile tests were conducted on permeability-exposed and as-received samples. Hydrogen-methane leakage experiments were also performed. The results show no selective leakage of hydrogen via Poiseuille, turbulent, or orifice flow (through leaks) on the distribution of blends of hydrogen and methane. The data collected show that the polyethylene pipe is 4 to 6 times more permeable to hydrogen than to methane.

Jasionowski, W. J.; Huang, H. D.

1980-01-01

348

Organic hydrogen gas sensor with palladium-coated ?-phase poly(vinylidene fluoride) thin films  

NASA Astrophysics Data System (ADS)

We have proposed an organic hydrogen gas sensor in which palladium (Pd)-coated ?-phase poly(vinylidene fluoride) (PVDF) films are utilized. Volume expansion of the Pd thin film caused by absorption of hydrogen gas is monitored by a piezoelectric thin film of PVDF attached to the Pd films. We have developed a simple method of synthesizing ?-phase PVDF films from ?-phase PVDF powder by using a wet process in which a mixture of acetone and hexamethylphosphoric triamide is used as the solvent for the PVDF powder. The sensor works by itself at room temperature without a power source.

Imai, Yuji; Kimura, Yasuo; Niwano, Michio

2012-10-01

349

Probing Vitamine C, Aspirin and Paracetamol in the Gas Phase: High Resolution Rotational Studies  

Microsoft Academic Search

A solid sample of Vitamin C (m.p. 190°C) vaporized by laser ablation has been investigated in gas phase and characterized through their rotational spectra. Two spectroscopy techniques has been used to obtain the spectra: a new design of broadband chirped pulse Fourier transform microwave spectroscopy with in-phase\\/quadrature-phase-modulation passage-acquired-coherence technique (IMPACT) and conventional laser ablation molecular beam Fourier transform microwave spectroscopy

S. Mata; C. Cabezas; M. Varela; I. Pena; A. Nino; J. C. López; J. L. Alonso; J.-U. Grabow

2011-01-01

350

Two-phase turbine engines. [using gas-liquid mixture accelerated in nozzles  

NASA Technical Reports Server (NTRS)

A description is given of a two-phase turbine which utilizes a uniform mixture of gas and liquid accelerated in nozzles of the types reported by Elliott and Weinberg (1968). The mixture acts directly on an axial flow or tangential impulse turbine or is separated into gas and liquid streams which operate separately on a gas turbine and a hydraulic turbine. The basic two-phase cycles are examined, taking into account working fluids, aspects of nozzle expansion, details of turbine cycle operation, and the effect of mixture ratio variation. Attention is also given to two-phase nozzle efficiency, two-phase turbine operating characteristics and efficiencies, separator turbines, and impulse turbine experiments.

Elliott, D. G.; Hays, L. G.

1976-01-01

351

Deposition nucleation viewed as homogeneous or immersion freezing in pores and cavities  

NASA Astrophysics Data System (ADS)

Heterogeneous ice nucleation is an important mechanism for the glaciation of mixed phase clouds and may also be relevant for cloud formation and dehydration at the cirrus cloud level. It is thought to proceed through different mechanisms, namely contact, condensation, immersion and deposition nucleation. Supposedly, deposition nucleation is the only pathway which does not involve liquid water but occurs by direct water vapor deposition on a surface. This study challenges this classical view by putting forward the hypothesis that what is called deposition nucleation is in fact homogeneous or immersion nucleation occurring in pores and cavities that may form between aggregated primary particles and fill with water at relative humidity RHw < 100% because of the inverse Kelvin effect. Evidence for this hypothesis of pore condensation and freezing (PCF) originates from a number of only loosely connected scientific areas. The prime example for PCF is ice nucleation in clay minerals and mineral dusts, for which the data base is best. Studies on freezing in confinement carried out on mesoporous silica materials such as SBA-15, SBA-16, MCM-41, zeolites and KIT have shown that homogeneous ice nucleation occurs abruptly at T=230-235 K in pores with diameters (D) of 3.5-4 nm or larger but only gradually at T=210-230 K in pores with D=2.5-3.5 nm. Melting temperatures in pores are depressed by an amount that can be described by the Gibbs-Thomson equation. Water adsorption isotherms of MCM-41 show that pores with D=3.5-4 nm fill with water at RHw = 56-60% in accordance with an inverse Kelvin effect. Water in such pores should freeze homogeneously for T < 235 K even before relative humidity with respect to ice (RHi) reaches ice saturation. Ice crystal growth by water vapor deposition from the gas phase is therefore expected to set in as soon as RHw > 100%. Pores with D > 7.5 nm fill with water at RHi > 100% for T < 235 K and are likely to freeze homogeneously as soon as they are filled with water. Water in pores can freeze in immersion mode at T > 235 K if the pore walls contain an active site. Pore analysis of clay minerals shows that kaolinites exhibit pore structures with pore diameters of 20-50 nm. The mesoporosity of illites and montmorillonites is characterized by pores with T = 2-5 nm. The number and size of pores is distinctly increased in acid treated montmorillonites like K10. Many clay minerals and mineral dusts show a strong increase in ice nucleation efficiency when temperature is decreased below 235 K. Such an increase is difficult to explain when ice nucleation is supposed to occur by a deposition mechanism, but evident when assuming freezing in pores, because for homogeneous ice nucleation only small pore volumes are needed, while heterogeneous ice nucleation requires larger pore structures to contain at least one active site for immersion nucleation. Together, these pieces of evidence strongly suggest that ice nucleation within pores should be the prevailing freezing mechanism of clay minerals for RHw below water saturation. Extending the analysis to other types of ice nuclei shows that freezing in pores and cracks is probably the prevailing ice nucleation mechanism for glassy and volcanic ash aerosols at RHw below water saturation. Freezing of water in carbon nanotubes might be of significance for ice nucleation by soot aerosols. No case could be identified that gives clear evidence of ice nucleation by water vapor deposition on a solid surface. Inspection of ice nuclei with a close lattice match to ice, such as silver iodide or SnomaxTM, show that for high ice nucleation efficiency below water saturation the presence of impurities or cracks on the surface may be essential. Soluble impurities promote the formation of a liquid phase below water saturation in patches on the surface or as a complete surface layer that offers an environment for immersion freezing. If porous aerosol particles come in contact with semivolatile vapors, these will condense preferentially in pores before a coating on

Marcolli, C.

2013-06-01

352

Homogeneous Dislocation Nucleation  

NASA Astrophysics Data System (ADS)

We perform atomistic computer simulations to study the mechanism of homogeneous dislocation nucleation (HDN) in a 2D hexagonal crystalline film under circular indentation. The nucleation process is governed by vanishing of energy associated with a single normal mode. For fixed film thickness, L, the spatial extent, ?, of the critical mode grows with indenter radius, R. For fixed R/L, ? scales roughly as ?˜L^0.4. We perform a mesoscale analysis to determine the lowest energy normal mode for regions of varying radius, rmeso, centered on the critical mode's core. The energy of the lowest normal mode ?meso->0 rapidly as rmeso->?. The lowest mode shows a spatial extent, ?meso, which increases sublinearly for rmeso<=? and saturates at rmeso 1.5; ?. We demonstrate that the ?meso/ ? versus rmeso/ ? curve is universal (independent of L or R). Hence small regions, rmeso<=?, can reveal the presence of incipient instability but give excellent estimates for the critical mode's energy and spatial extent only for rmeso>=1.5; ?. Thus HDN is a quasi-local phenomenon.

Hasan, Asad; Maloney, Craig

2012-02-01

353

Nucleation of Nuclear Bodies  

PubMed Central

The nucleus is a complex organelle containing numerous highly dynamic, structurally stable domains and bodies, harboring functions that have only begun to be defined. However, the molecular mechanisms for their formation are still poorly understood. Recently it has been shown that a nuclear body can form de novo by self-organization. But little is known regarding what triggers the formation of a nuclear body and how subsequent assembly steps are orchestrated. Nuclear bodies are frequently associated with specific active gene loci that directly contribute to their formation. Both coding and noncoding RNAs can initiate the assembly of nuclear bodies with which they are physiologically associated. Thus, the formation of nuclear bodies occurs via recruitment and consequent accumulation of resident proteins in the nuclear bodies by nucleating RNA acting as a seeder. In this chapter I describe how to set up an experimental cell system to probe de novo biogenesis of a nuclear body by nucleating RNA and nuclear body components tethered on chromatin. PMID:23980018

Dundr, Miroslav

2014-01-01

354

Lipase hydration state in the gas phase: Sorption isotherm measurements and inverse gas chromatography.  

E-print Network

chromatography. Zsuzsanna Marton1 , Ludovic Chaput1 , Guillaume Pierre1 and Marianne Graber1 1 Université de la Rochelle, Cedex 01, France. Keywords: Water, Lipase, Adsorption, Inverse Gas Chromatography, Solid@univ-lr.fr Fax : +33 5 46 45 82 65 Abbreviations: IGC, Inverse Gas Chromatography aW, water thermodynamic

Paris-Sud XI, Université de

355

Temperature-dependent phase behavior and the crystal-forming nucleation process of ethyl 4-fluoro-2,3-dihydroxystearate monolayers.  

PubMed

The phase behavior of enantiomeric compounds as well as mixtures of enantiopure and racemic diastereomers of ethyl 4-fluoro-2,3-dihydroxystearates has been investigated using surface pressure-area isotherms and Brewster angle microscopy (BAM). All mixtures exhibit a small plateau region within the surface pressure-area isotherm at 20 degrees C, whereas the enantiopure compound shows an isotherm behavior similar to that of fatty acids. Corresponding to the film balance measurements, the BAM images demonstrate different shapes of the domains within the coexistence region of the liquid-condensed/liquid-expanded phase. The domain structures of the monolayers were visualized after Langmuir-Blodgett transfer on mica sheets by scanning force microscopy (SFM). From the SFM images it becomes obvious that small crystallites are formed for all investigated compounds; however, their molecular assembly is diverse for different enantiomers. Variations in the phase behavior can be correlated with interactions between the polar molecular moieties and the subphase and altered intermolecular interactions. Molecular modeling calculations were applied to elucidate the structural organization of these intermolecular interactions. Ab initio calculations of the minima conformers of (S,S,R)- and (S,S,S)-ethyl 4-fluoro-2,3-dihydroxystearates have been performed to predict with the HARDPACK program the two-dimensional lattice structure based on the P1 space group. These calculations showed that intermolecular hydrogen bridges are crucial for the interactions within and between the molecules. PMID:17279670

Steffens, Silke; Höweler, Udo; Jödicke, Tim; Oldendorf, Jens; Rudert, Rainer; Haufe, Günter; Galla, Hans-Joachim

2007-02-13

356

Spatial point pattern analysis applied to bubble nucleation in silicate melts  

NASA Astrophysics Data System (ADS)

Experimental bubble nucleation studies are used for determining the nucleation mechanism as a function of experimental conditions, the resulting bubble number density, and can also yield estimates of the melt-vapor surface tension. This provides important information on gas exsolution in silicate melts, which can be applied towards understanding magmatic degassing in volcanic conduits. At present, determination of nucleation processes in tiny experimental samples relies upon visual observations. To improve the characterization of the spatial distribution of bubbles, we present a new application of spatial point pattern analysis. This technique allows the quantitative description of the spatial distribution of nucleation sites and has the potential to distinguish between homogeneous, heterogeneous, and multiple nucleation events. Since point pattern analysis highlights clustering or spatial regularity among objects, it may improve our understanding of the melt structure underlying the spatial distribution of nucleation sites, as well as interactions between bubble populations resulting from different nucleation pulses within a single experimental sample.

Mongrain, Joanna; Larsen, Jessica F.

2009-09-01

357

Phase transitions in copper(3)gold, silver iodide, and n-alkanes  

Microsoft Academic Search

We have studied phase transitions in two lattice systems, Cu3Au and AgI, using a discrete version of density functional theory and gas-liquid nucleation in n-alkanes using a density functional theory for a polyatomic system. First, the order-disorder transition and bulk and surface nucleation in Cu3Au have been investigated. A continuous surface transition occurs due to a smaller number of surface

Chaok Seok

1998-01-01

358

Gas chromatography on wall-coated open-tubular columns with ionic liquid stationary phases.  

PubMed

Ionic liquids have moved from novel to practical stationary phases for gas chromatography with an increasing portfolio of applications. Ionic liquids complement conventional stationary phases because of a combination of thermophysical and solvation properties that only exist for ionic solvents. Their high thermal stability and low vapor pressure makes them suitable as polar stationary phases for separations requiring high temperatures. Ionic liquids are good solvents and can be used to expand the chemical space for separations. They are the only stationary phases with significant hydrogen-bond acidity in common use; they extend the hydrogen-bond basicity of conventional stationary phases; they are as dipolar/polarizable as the most polar conventional stationary phases; and some ionic liquids are significantly less cohesive than conventional polar stationary phases. Problems in column coating techniques and related low column performance, column activity, and stationary phase reactivity require further exploration as the reasons for these features are poorly understood at present. PMID:24690306

Poole, Colin F; Lenca, Nicole

2014-08-29

359

Gas-Phase Database for Quantitative Infrared Spectroscopy  

Microsoft Academic Search

The National Institute of Standards and Technology (NIST) and the Pacific Northwest National Laboratory (PNNL) are each creating quantitative databases containing the vapor-phase infrared spectra of pure chemicals. The digital databases have been created with both laboratory and remote-sensing applications in mind. A spectral resolution of 0.1 cm¹ was selected to avoid degrading sharp spectral features, while also realizing that

Steven W. Sharpe; Timothy J. Johnson; Robert L. Sams; Pamela M. Chu; George C. Rhoderick; Patricia A. Johnson

2004-01-01

360

Comparison of Gradient Theory with Classical Nucleation Theory  

NASA Astrophysics Data System (ADS)

We applied gradient theory to the gas-liquid nucleation process. We studied spherical droplets in a van der Waals fluid and calculated droplet density profiles for various supersaturations. From the density profiles, we calculated pressure tensors, radius of surface of tension, number of molecules in critical nucleus, and reversible work. We compared these results with those obtained from the classical nucleation theory. As is well known, gradient theory predicts that at the spinodal the free energy barrier to nucleation vanishes while the radius of the critical fluctuation diverges. Classical theory predicts a finite nucleation barrier and small critical size at the spinodal. We found that the excess number of molecules in the critical fluctuation predicted by gradient theory is small and is close to the classical value near the spinodal. Thus, in this sense, gradient theory also predicts a small critical fluctuation and is in qualitative agreement with the classical theory on this point.

Li, J.-S.; Obeidat, A.; Wilemski, G.

2001-03-01

361

Experimental evidence for seismically initiated gas bubble nucleation and growth in groundwater as a mechanism for coseismic borehole water level rise and remotely triggered seismicity  

NASA Astrophysics Data System (ADS)

in borehole water levels and remotely triggered seismicity occur in response to near and distant earthquakes at locations around the globe, but the mechanisms for these phenomena are not well understood. Experiments were conducted to show that seismically initiated gas bubble growth in groundwater can trigger a sustained increase in pore fluid pressure consistent in magnitude with observed coseismic borehole water level rise, constituting a physically plausible mechanism for remote triggering of secondary earthquakes through the reduction of effective stress in critically loaded geologic faults. A portion of the CO2 degassing from the Earth's crust dissolves in groundwater where seismic Rayleigh and P waves cause dilational strain, which can reduce pore fluid pressure to or below the bubble pressure, triggering CO2 gas bubble growth in the saturated zone, indicated by a spontaneous buildup of pore fluid pressure. Excess pore fluid pressure was measured in response to the application of 0.1-1.0 MPa, 0.01-0.30 Hz confining stress oscillations to a Berea sandstone core flooded with initially subsaturated aqueous CO2, under conditions representative of a confined aquifer. Confining stress oscillations equivalent to the dynamic stress of the 28 June 1992 Mw 7.3 Landers, California, earthquake Rayleigh wave as it traveled through the Long Valley caldera, and Parkfield, California, increased the pore fluid pressure in the Berea core by an average of 36 ± 15 cm and 23 ± 15 cm of equivalent freshwater head, respectively, in agreement with 41.8 cm and 34 cm rises recorded in wells at those locations.

Crews, Jackson B.; Cooper, Clay A.

2014-09-01

362

Evaluation of low-cost gas-sensor technology. Phase 1. Final report, January-April 1986  

Microsoft Academic Search

The results of Phase 1 of an investigation of the use of low-cost gas detection and alarm instruments by utilities throughout the world are reported. Because Japan stands out as the only country in the world that has established a mass market for domestic and commercial gas-leak alarms, incomplete combustion monitors, and automatic gas shutoff systems, the Phase 1 report

P. K. Clifford; M. G. Dorman

1986-01-01

363

Modelling non-equilibrium secondary organic aerosol formation and evaporation with the aerosol dynamics, gas- and particle-phase chemistry kinetic multi-layer model ADCHAM  

NASA Astrophysics Data System (ADS)

We have developed the novel Aerosol Dynamics, gas- and particle-phase chemistry model for laboratory CHAMber studies (ADCHAM). The model combines the detailed gas phase Master Chemical Mechanism version 3.2, an aerosol dynamics and particle phase chemistry module (which considers acid catalysed oligomerization, heterogeneous oxidation reactions in the particle phase and non-ideal interactions between organic compounds, water and inorganic ions) and a kinetic multilayer module for diffusion limited transport of compounds between the gas phase, particle surface and particle bulk phase. In this article we describe and use ADCHAM to study: (1) the mass transfer limited uptake of ammonia (NH3) and formation of organic salts between ammonium (NH4+) and carboxylic acids (RCOOH), (2) the slow and almost particle size independent evaporation of ?-pinene secondary organic aerosol (SOA) particles, and (3) the influence of chamber wall effects on the observed SOA formation in smog chambers. ADCHAM is able to capture the observed ?-pinene SOA mass increase in the presence of NH3(g). Organic salts of ammonium and carboxylic acids predominantly form during the early stage of SOA formation. These salts contribute substantially to the initial growth of the homogeneously nucleated particles. The model simulations of evaporating ?-pinene SOA particles support the recent experimental findings that these particles have a semi-solid tar like amorphous phase state. ADCHAM is able to reproduce the main features of the observed slow evaporation rates if low-volatility and viscous oligomerized SOA material accumulates in the particle surface layer upon evaporation. The evaporation rate is mainly governed by the reversible decomposition of oligomers back to monomers. Finally, we demonstrate that the mass transfer limited uptake of condensable organic compounds onto wall deposited particles or directly onto the Teflon chamber walls of smog chambers can have profound influence on the observed SOA formation. During the early stage of the SOA formation the wall deposited particles and walls themselves serve as a SOA sink from the air to the walls. However, at the end of smog chamber experiments the semi-volatile SOA material may start to evaporate from the chamber walls. With these three model applications, we demonstrate that several poorly quantified processes, i.e. mass transport limitations within the particle phase, oligomerization, heterogeneous oxidation, organic salt formation, and chamber wall effects can have substantial influence on the SOA formation, lifetime, chemical and physical particle properties, and their evolution. In order to constrain the uncertainties related to these processes, future experiments are needed where as many of the influential variables as possible are varied. ADCHAM can be a valuable model tool in the design and analysis of such experiments.

Roldin, P.; Eriksson, A. C.; Nordin, E. Z.; Hermansson, E.; Mogensen, D.; Rusanen, A.; Boy, M.; Swietlicki, E.; Svenningsson, B.; Zelenyuk, A.; Pagels, J.

2014-01-01

364

Crystallization of Ge2Sb2Te5 nanometric phase change material clusters made by gas-phase condensation  

NASA Astrophysics Data System (ADS)

The crystallization behavior of Ge2Sb2Te5 nanometric clusters was studied using X-ray diffraction with in situ annealing. Clusters were made using a sputtering gas-phase condensation source, which allowed for the growth of well-defined, contaminant-free, and isolated clusters. The average size for the clusters is 5.7 ± 1 nm. As-deposited amorphous clusters crystallize in the fcc cubic phase at 180 °C, while for thin films, the phase change temperature is 155 °C. This observation illustrates the scalability of the Ge2Sb2Te5 phase change from the amorphous to the cubic state in three-dimensionally confined systems in this size range.

Ghezzi, G. E.; Morel, R.; Brenac, A.; Boudet, N.; Audier, M.; Fillot, F.; Maitrejean, S.; Hippert, F.

2012-12-01

365

Efficient and directed peptide bond formation in the gas phase via ion/ion reactions  

PubMed Central

Amide linkages are among the most important chemical bonds in living systems, constituting the connections between amino acids in peptides and proteins. We demonstrate the controlled formation of amide bonds between amino acids or peptides in the gas phase using ion/ion reactions in a mass spectrometer. Individual amino acids or peptides can be prepared as reagents by (i) incorporating gas phase–labile protecting groups to silence otherwise reactive functional groups, such as the N terminus; (ii) converting the carboxyl groups to the active ester of N-hydroxysuccinimide; and (iii) incorporating a charge site. Protonation renders basic sites (nucleophiles) unreactive toward the N-hydroxysuccinimide ester reagents, resulting in sites with the greatest gas phase basicities being, in large part, unreactive. The N-terminal amines of most naturally occurring amino acids have lower gas phase basicities than the side chains of the basic amino acids (i.e., those of histidine, lysine, or arginine). Therefore, reagents may be directed to the N terminus of an existing “anchor” peptide to form an amide bond by protonating the anchor peptide’s basic residues, while leaving the N-terminal amine unprotonated and therefore reactive. Reaction efficiencies of greater than 30% have been observed. We propose this method as a step toward the controlled synthesis of peptides in the gas phase. PMID:24474750

McGee, William M.; McLuckey, Scott A.

2014-01-01

366

Changing the shape of molecular ions: photoisomerization action spectroscopy in the gas phase.  

PubMed

A new approach for studying the photoisomerization of molecular ions in the gas phase is described. Packets of molecular ions are injected into a drift tube filled with helium buffer gas, where they are irradiated with tunable laser light. Photoisomerization changes the ions' cross section for collisions with helium atoms so that they arrive at the ion detector slightly earlier or later than the parent ions. By monitoring the photo-isomer peak as a function of laser wavelength one can record an action spectrum that is related to the ions' absorption spectrum modulated by the photoisomerization probability. The approach is demonstrated using the polymethine dye HITC (1,3,3,1',3',3'-hexamethylindotricarbocyanine). The data show that both trans and cis forms of HITC(+) exist in the gas phase with trans?cis photoisomerization predominating over the 550-710 nm range and cis?trans photoisomerization occurring over the 735-770 nm range. The gas-phase photoisomerization action spectrum is comparable to the absorption spectra of trans HITC and cis HTIC in the condensed phase, but with the absorption peaks shifted to shorter wavelength. The gas-phase photoisomerization action spectrum of the (HITC)2(2+) dication dimer is also reported. (HITC)2(2+) cations photoisomerize over the 550-770 nm range to form more compact structures. PMID:23674245

Adamson, B D; Coughlan, N J A; Continetti, R E; Bieske, E J

2013-06-28

367

Factors controlling the ice nucleating abilities of ?-pinene SOA particles  

NASA Astrophysics Data System (ADS)

The ice nucleation abilities of fresh, water-soluble, internally mixed, and photochemically oxidized ?-pinene secondary organic aerosol (SOA) particles were investigated at cirrus cloud temperatures in a continuous flow diffusion chamber. SOA sampled from a flow tube (SOA-fresh-FT) mimicked freshly generated particles, while the water-soluble organic compound fraction from a FT and smog chamber (SOA-WSOC-FT, SOA-WSOC-SC) mimicked cloud-processed particles. SOA-fresh-FT, SOA-WSOC-FT, and SOA-WSOC-SC particles were not highly active at nucleating ice between 233 K and 213 K, with activation onsets (i.e., 0.1% of particles forming ice) at or slightly above the theoretical homogeneous freezing line. A significant increase in the O/C of SOA-WSOC-SC via aqueous phase OH oxidation did not modify the ice nucleation abilities, indicating that the detailed composition of the particles is not of paramount importance to their ice nucleating abilities. Instead, precooling the SOA-WSOC-FT and SOA-WSOC-SC particles to 233 K dropped their ice nucleation onsets by up to 20% relative humidity with respect to ice, with lower temperatures likely driving the particles to be more viscous and solid-like. However, it is possible that preactivation contributed to the reduction of the ice nucleation onsets. Particles composed of both SOA-WSOC and ammonium sulfate (AS) were significantly less active in the deposition nucleation mode than pure, solid AS particles.

Ladino, L. A.; Zhou, S.; Yakobi-Hancock, J. D.; Aljawhary, D.; Abbatt, J. P. D.

2014-07-01

368

Numerical Computation of Flame Spread over a Thin Solid in Forced Concurrent Flow with Gas-phase Radiation  

NASA Technical Reports Server (NTRS)

Excerpts from a paper describing the numerical examination of concurrent-flow flame spread over a thin solid in purely forced flow with gas-phase radiation are presented. The computational model solves the two-dimensional, elliptic, steady, and laminar conservation equations for mass, momentum, energy, and chemical species. Gas-phase combustion is modeled via a one-step, second order finite rate Arrhenius reaction. Gas-phase radiation considering gray non-scattering medium is solved by a S-N discrete ordinates method. A simplified solid phase treatment assumes a zeroth order pyrolysis relation and includes radiative interaction between the surface and the gas phase.

Jiang, Ching-Biau; T'ien, James S.

1994-01-01

369

Measurements of liquid-phase turbulence in gas-liquid two-phase flows using particle image velocimetry  

NASA Astrophysics Data System (ADS)

Liquid-phase turbulence measurements were performed in an air-water two-phase flow loop with a circular test section of 50 mm inner diameter using a particle image velocimetry (PIV) system. An optical phase separation method--planar laser-induced fluorescence (PLIF) technique—which uses fluorescent particles and an optical filtration technique, was employed to separate the signals of the fluorescent seeding particles from those due to bubbles and other noises. An image pre-processing scheme was applied to the raw PIV images to remove the noise residuals that are not removed by the PLIF technique. In addition, four-sensor conductivity probes were adopted to measure the radial distribution of the void fraction. Two benchmark tests were performed: the first was a comparison of the PIV measurement results with those of similar flow conditions using thermal anemometry from previous studies; the second quantitatively compared the superficial liquid velocities calculated from the local liquid velocity and void fraction measurements with the global liquid flow rate measurements. The differences of the superficial liquid velocity obtained from the two measurements were bounded within ±7% for single-phase flows and two-phase bubbly flows with the area-average void fraction up to 18%. Furthermore, a preliminary uncertainty analysis was conducted to investigate the accuracy of the two-phase PIV measurements. The systematic uncertainties due to the circular pipe curvature effects, bubble surface reflection effects and other potential uncertainty sources of the PIV measurements were discussed. The purpose of this work is to facilitate the development of a measurement technique (PIV-PLIF) combined with image pre-processing for the liquid-phase turbulence in gas-liquid two-phase flows of relatively high void fractions. The high-resolution data set can be used to more thoroughly understand two-phase flow behavior, develop liquid-phase turbulence models, and assess high-fidelity codes for multi-phase flows.

Zhou, Xinquan; Doup, Benjamin; Sun, Xiaodong

2013-12-01

370

Surface nanobubbles nucleate microdroplets.  

PubMed

When a hydrophobic solid is in contact with water, surface nanobubbles often form at the interface. They have a lifetime many orders of magnitude longer than expected. Here, we show that they even withstand a temperature increase to temperatures close to the boiling point of bulk water; i.e., they do not nucleate larger bubbles ("superstability"). On the contrary, when the vapor-liquid contact line passes a nanobubble, a liquid film remains around it, which, after pinch-off, results in a microdroplet in which the nanobubbles continue to exist. Finally, the microdroplet evaporates and the nanobubble consequently bursts. Our results support that pinning plays a crucial role for nanobubble stability. PMID:24765973

Zhang, Xuehua; Lhuissier, Henri; Sun, Chao; Lohse, Detlef

2014-04-11

371

Nucleation and growth of cracks in vitreous-bonded aluminum oxide at elevated temperatures  

SciTech Connect

The nucleation and growth of cracks was studied at elevated temperatures on a grade of vitreous-bonded aluminium oxide that contained approx. =8 vol% glass at the grain boundaries. Cracks were observed to nucleate within the vitreous phase, close to the tensile surface of the flexural test specimens used in these experiments. Crack nucleation occurred at a strain of approx. =0.08% to 0.12% which corresponded to a crack nucleation time of approx. =35% of the time to failure by creep rupture. Once nucleated, cracks propagated along grain boundaries, as long as the stress for crack propagation was maintained. The crack velocity for cracks that were nucleated by the creep process was found to be linearly proportional to the apparent stress intensity factor, whereas for cracks that were nucleated by indentation, the crack velocity was proportional to the fourth power of the apparent stress intensity factor.

Jakus, K.; Wiederhorn, S.M.; Hockey, B.J.

1986-10-01

372

Liquid-gas mixed phase in nuclear matter at finite temperature  

E-print Network

We explore the geometrical structure of Liquid-gas (LG) mixed phase which is relevant to nuclear matter in the crust region of compact stars or supernovae. To get the equation of state (EOS) of the system, the Maxwell construction is found to be applicable to symmetric nuclear matter, where protons and neutrons behave simultaneously. For asymmetric nuclear matter, on the other hand, the phase equilibrium can be obtained by fully solving the Gibbs conditions since the components in the L and G phases are completely different. We also discuss the effects of surface and the Coulomb interaction on the mixed phase.

Toshiki Maruyama; Toshitaka Tatsumi

2010-09-07

373

Profiling of gas turbine blade using phase shifting Talbot interferometric technique  

NASA Astrophysics Data System (ADS)

In this paper we present phase shifting Talbot interferometry for the measurement of surface topography of the gas turbine blades. Interferograms of the different steps are recorded and displayed on the computer monitor using digital techniques. Presence of the harmonic components in the phase map due to the Ronchi gratings are removed by using Fourier filtering. The variation of the surface height at the different points of the objects is obtained by generating the phase map. The results obtained by phase shifting Talbot interferometric techniques are in good agreements with that of the measured by the manually controlled co- ordinate measuring machine. The critical analysis of results alongwith error analysis is presented.

Shakher, Chandra; Mehta, D. S.; Mirza, Saba; Singh, Priti

2005-06-01

374

OMVPE growth and gas-phase reactions of AlGaN for UV emitters  

SciTech Connect

Gas-phase parasitic reactions among TMG, TMA, and NH3, are investigated by monitoring of the growth rate/incorporation efficiency of GaN and AlN using an in-situ optical reflectometer. It is suggested that gas phase adduct (TMA: NH{sub 3}) reactions not only reduce the incorporation efficiency of TMA but also affect the incorporation behavior of TMGa. The observed phenomena can be explained by either a synergistic gas-phase scavenging effect or a surface site-blocking effect. Relatively low reactor pressures (30--50 Torr) are employed to grow an AlGaN/GaN QW p-n diode structure. The UV emission at 354 nm (FWHM {approximately} 6 nm) represents the first report of LED operation from an indium-free GaN QW diode.

Han, J.; Figiel, J.J.; Crawford, M.H.; Banas, M.A.; Bartram, M.E.; Biefeld, R.M. [Sandia National Labs., Albuquerque, NM (United States); Song, Y.K.; Nurmikko, A.V. [Brown Univ., Providence, RI (United States). Div. of Engineering

1998-06-01

375

Gas phase glyoxal and methylglyoxal yields from the oxidation of isoprene and first generation products  

NASA Astrophysics Data System (ADS)

?-dicarbonyls such as glyoxal and methylglyoxal are of increasing interest due to their importance in atmospheric processes and their ability to partition from the gas to aerosol phase. Isoprene oxidation is a major source of glyoxal and methylglyoxal in the atmosphere. However, the reaction pathways for these compounds are not well known, nor are the yields. Incorporation of the formation rates and yields of these compounds determined from our studies will allow us to improve chemical models that include isoprene oxidation. To achieve this, we performed experiments at the Caltech environmental chambers to determine the gas phase yields of glyoxal, methylglyoxal, and formaldehyde from isoprene and its primary reaction products, methyl vinyl ketone and methacrolein, under varied oxidation conditions. Gas phase glyoxal, methylglyoxal, and formaldehyde yields from the oxidation of these precursors will be presented as well as analysis of first generation glyoxal formation from isoprene oxidation.

Galloway, Melissa; Loza, Christine; Yee, Lindsay; Chan, Arthur; Crounse, John; Wennberg, Paul; Seinfeld, John; Keutsch, Frank

2010-05-01

376

Device for two-dimensional gas-phase separation and characterization of ion mixtures  

DOEpatents

The present invention relates to a device for separation and characterization of gas-phase ions. The device incorporates an ion source, a field asymmetric waveform ion mobility spectrometry (FAIMS) analyzer, an ion mobility spectrometry (IMS) drift tube, and an ion detector. In one aspect of the invention, FAIMS operating voltages are electrically floated on top of the IMS drift voltage. In the other aspect, the FAIMS/IMS interface is implemented employing an electrodynamic ion funnel, including in particular an hourglass ion funnel. The present invention improves the efficiency (peak capacity) and sensitivity of gas-phase separations; the online FAIMS/IMS coupling creates a fundamentally novel two-dimensional gas-phase separation technology with high peak capacity, specificity, and exceptional throughput.

Tang, Keqi (Richland, WA); Shvartsburg, Alexandre A. (Richland, WA); Smith, Richard D. (Richland, WA)

2006-12-12

377

Measurement of gas-phase ionic mercury(II) species in ambient air  

SciTech Connect

One of the important questions in the biogeochemical cycling of mercury is the speciation of mercury in the atmosphere. Although a large fraction of Hg in ambient air is Hg(O), a small fraction is believed to be gas-phase Hg(II). This fraction is highly water-soluble and thus is important to explaining the high concentration of Hg in precipitation. We have developed a novel technique for measuring gas-phase Hg(II), using a high-flow refluxing mist chamber to trap the water-soluble Hg(II) in an aerosol mist. Measured concentrations of gas-phase Hg(II) in ambient air are generally in the range 0.05-0.1 ng/m{sup 3}, or 2-4% of the total gaseous Hg. In this talk, representative data under different atmospheric and geographic conditions will be presented, along with a summary of some of the experimental difficulties and unanswered questions.

Stratton, W.J. [Earlharn College, Richmond, IN (United States); Lindberg, S.E. [Oak Ridge National Lab., TN (United States)

1995-12-31

378

Modeling of the gas-phase chemistry in C-H-O gas mixtures for diamond chemical vapor deposition  

NASA Astrophysics Data System (ADS)

The boundaries of the diamond deposition region in the C-H-O (Bachmann) atomic phase composition diagram have been reproduced successfully for 38 different C, H, and O containing gas mixtures using the CHEMKIN computer package, together with just two criteria—a minimum mole fraction of methyl radicals [CH3] and a limiting value of the [H]/[C2H2] ratio. The diamond growth/no-growth boundary coincides with the line along which the input mole fractions of C and O are equal. For every gas mixture studied, no-growth regions are found to coincide with a negligible (<10-10) mole fraction of CH3 radicals, while for gas mixtures lying within the diamond growth region the CH3 mole fraction is ˜10-7. Each no-growth?diamond growth boundary is seen to be accompanied by a 2-3 order of magnitude step in CH3 mole fraction. The boundary between diamond and nondiamond growth is less clearly defined, but can be reproduced by assuming a critical, temperature dependent [H]/[C2H2] ratio (0.2, in the case that Tgas=2000 K) that reflects the crucial role of H atoms in the etching of nondiamond phases. The analysis allows prediction of the composition process window for good quality diamond growth for all stable input gas mixtures considered in this study.

Petherbridge, James R.; May, Paul W.; Ashfold, Michael N. R.

2001-05-01

379

Molecular simulation of crystal nucleation in n-octane melts  

E-print Network

Homogeneous nucleation of the crystal phase in n-octane melts was studied by molecular simulation with a realistic, united-atom model for n-octane. The structure of the crystal phase and the melting point of n-octane were ...

Yi, Peng

380

Gas phase investigations of sulfonium salts by electrospray ft-icr\\/ms  

Microsoft Academic Search

Twelve sulfonium salts were studied by electrospray Fourier transform ion cyclotron resonance mass spectrometry. Collisionally activated dissociation, CAD, reactions, using neutral argon as the collision gas, were performed to investigate dissociation pathways in the gas phase and to study the stabilizing\\/destabilizing effects of electron donating\\/withdrawing substituents on the sulfonium ions. Ion-molecule reactions were attempted to identify SN2 reaction mechanisms, but

Alan R. Katritzky; Petia A. Shipkova; Clifford H. Watson; John R. Eyler; Dennis N. Kevill

1997-01-01

381

Fermi-liquid behavior of the normal phase of a strongly interacting gas of cold atoms.  

PubMed

We measure the magnetic susceptibility of a Fermi gas with tunable interactions in the low-temperature limit and compare it to quantum Monte Carlo calculations. Experiment and theory are in excellent agreement and fully compatible with the Landau theory of Fermi liquids. We show that these measurements shed new light on the nature of the excitations of the normal phase of a strongly interacting Fermi gas. PMID:21699311

Nascimbène, S; Navon, N; Pilati, S; Chevy, F; Giorgini, S; Georges, A; Salomon, C

2011-05-27

382

Use of a Climate-Controlled Chamber to Investigate the Fate of Gas-Phase Anthracene  

Microsoft Academic Search

Air-surface exchange of semivolatile organic compounds (SOC) isan important factor controlling the gas-phase concentrations ofthese compounds. In this study, the uptake of gas-phaseanthracene, an SOC, by the leaves of Ficus benjamina wasexamined in a large (30 m3) environmentally-controlledchamber. To investigate the effect of climate on air\\/leafexchange, the air flow-rate, temperature, and relative humidityin the chamber was controlled and continually monitored.

Aaron M. Peck; Keri C. Hornbuckle

2003-01-01

383

Experimental and gas phase modeling of nanocrystalline diamond films grown on titanium alloys for biomedical applications  

Microsoft Academic Search

For biomedical applications, it is highly desirable to be able to deposit smooth adherent diamond films on various complex-shaped\\u000a substrates using the hot filament chemical vapor deposition technique (HFCVD). The properties of these films are affected\\u000a profoundly by process parameters such as filament temperature, gas composition, and pressure. In this study, we present an\\u000a insight into the gas phase chemistry

M. J. Jackson; A. N. Jones; W. Ahmed

2005-01-01

384

AN EXPERIMENTAL STUDY OF GAS HOLDUP IN TWO-PHASE BUBBLE COLUMNS WITH FOAMING LIQUIDS  

Microsoft Academic Search

Gas-liquid upward flow experiments have been performed in two bubble columns of different diameters (0.10 and 0.29 m,) using air as gas phase and several liquids: water, aqueous solutions of ethanol and glycerine, kerosene, and a solution of a surfactant in kerosene. The main goal of the study is the analysis of foaming systems, including the comparison of their behavior with

L. Z. PINO; M. M. YÉPEZ; A. E. SÁEZ; G. DE DRAGO

1990-01-01

385

Metal film deposition by gas-phase laser pyrolysis of nickel tetracarbonyl  

NASA Astrophysics Data System (ADS)

A new technique for the deposition of nickel metal films by gas-phase pyrolysis of nickel tetracarbonyl gas is described. A pulsed CO2 laser is used to form a reaction zone adjacent to a cold substrate, resulting in a rapidly quenched film. The technique relies on dielectric breakdown of a mixture of source and carrier gases and therefore lends itself to a variety of source gases and chemistries. Adherence data and compositional and structural analyses are presented.

Jervis, T. R.

1985-08-01

386

Challenges in Modeling Gas-Phase Flow in Microchannels: From Slip to Transition  

Microsoft Academic Search

It has long been recognized that the fluid mechanics of gas-phase microflows can differ significantly from the macroscopic world. Non-equilibrium effects such as rarefaction and gas-surface interactions need to be taken into account, and it is well known that the no-slip boundary condition of the Navier-Stokes equations is no longer valid. Following ideas proposed by Maxwell, it is generally accepted

Robert W. Barber; David R. Emerson

2006-01-01

387

Three-phase gas/oil/brine relative permeabilities measured under CO[sub 2] flooding conditions  

SciTech Connect

Steady-state three-phase gas/oil/brine relative permeabilities were measured in a carbonate core under CO[sub 2] flooding conditions. Results show that the relative permeability of each phase depends only on the saturation of that phase instead of on two saturations, as many previous studies have concluded. All previously reported gas/oil brine relative permeability studies have been conducted with low-pressure N[sub 2] gas or air. In this work, CO[sub 2] gas, oil, and brine were injected into a carbonate core at 71 C and 9.65 MPa so that the phase behavior and flow would be similar to reservoir conditions. Results show that significant differences exist between the three-phase gas/oil/brine relative permeabilities measured when the gas is CO[sub 2] and those measured when the gas was N[sub 2].

Dria, D.E.; Pope, G.A.; Sepehrnoori, K. (Univ. of Texas, Austin, TX (United States))

1993-05-01

388

Surface-enhanced nucleation of insulin amyloid fibrillation.  

PubMed

Proteins can interact with biological surfaces such as cell membrane, chaperones, cornea, bone, arteries, veins, and heart cavities of the cardiovascular system and also with non-biological surfaces including dialysis membranes and tubing, catheters, invasive surgical instruments, needles, and artificial implants. Fibrillation of amyloid proteins is implicated in many human diseases, including Alzheimer's, Parkinson's, and type II diabetes. Here, we show that heterogeneous surfaces accelerate the human insulin nucleation process that is the rate-determining step during amyloid fibril formation. The observed shorter lag (nucleation) phase correlates both with surface wettability and surface roughness. Surfaces promote faster nucleation possibly by increasing the local concentration of protein molecules. A composite parameter combining both surface wettability and roughness suggests that the ideal surface for slower nucleation should be hydrophilic and smooth. These findings provide a basis for designing suitable biomaterials and biomedical devices, especially those to resist amyloidosis. PMID:18267105

Nayak, Arpan; Dutta, Amit K; Belfort, Georges

2008-05-01

389

Intrinsic Gas-Phase Spin Relaxation of ^129Xe  

NASA Astrophysics Data System (ADS)

Hyperpolarized (HP) ^129Xe produced through spin-exchange optical pumping (SEOP) techniques is useful for many NMR and MRI applications. At gas densities typical for SEOP, fluctuations in the spin-rotation and chemical shift anisotropy interactions mediated by the formation and breakup of loosely bound ^129Xe-Xe molecules have recently been identified as the primary intrinsic spin relaxation mechanism, with T1 limits as short as 5 hours for samples of pure Xe. We have shown that this relaxation mechanism can be suppressed at high magnetic fields, leading to T1 relaxation times of 100 h at 14.1 T. Further results showed a near doubling of relaxation times with moderate temperature increases from 293 K to 393 K, implying a maximum intrinsic relaxation time of 9 h at 393 K. In the field regime practical for SEOP (2.8 mT), we observed ^129Xe relaxation times of nearly 5 hours in a 1 amagat Xe sample at 393 K. These results suggest a practical, low-field, non-cryogenic storage system that will provide Xe hold times much longer than those currently available from standard cryogenic storage systems on flow-through Xe polarizers.

Anger, B. C.; Solum, M. S.; Pugmire, R. J.; Saam, B.

2008-05-01

390

The interstellar gas-phase chemistry of HCN and HNC  

E-print Network

We review the reactions involving HCN and HNC in dark molecular clouds to elucidate new chemical sources and sinks of these isomers. We find that the most important reactions for the HCN-HNC system are Dissociative Recombination (DR) reactions of HCNH+ (HCNH+ + e-), the ionic CN + H3+, HCN + C+, HCN and HNC reactions with H+/He+/H3+/H3O+/HCO+, the N + CH2 reaction and two new reactions: H + CCN and C + HNC. We test the effect of the new rate constants and branching ratios on the predictions of gas-grain chemical models for dark cloud conditions. The rapid C + HNC reaction keeps the HCN/HNC ratio significantly above one as long as the carbon atom abundance remains high. However, the reaction of HCN with H3+ followed by DR of HCNH+ acts to isomerize HCN into HNC when carbon atoms and CO are depleted leading to a HCN/HNC ratio close to or slightly greater than 1. This agrees well with observations in TMC-1 and L134N taking into consideration the overestimation of HNC abundances through the use of the same rotati...

Loison, Jean-Christophe; Hickson, Kevin M

2014-01-01

391

Gas phase water in the surface layer of protoplanetary disks  

E-print Network

Recent observations of the ground state transition of HDO at 464 GHz towards the protoplanetary disk of DM Tau have detected the presence of water vapor in the regions just above the outer disk midplane (Ceccarelli et al 2005). In the absence of non-thermal desorption processes, water should be almost entirely frozen onto the grain mantles and HDO undetectable. In this Letter we present a chemical model that explores the possibility that the icy mantles are photo-desorbed by FUV (6eV water vapor above the disk midplane over the entire disk. Assuming a photo-desorption yield of 10^{-3}, the water abundance in this layer is predicted to be ~ 3 x 10^{-7} and the average H2O column density is ~ 1.6x 10^{15} cm^{-2}. The predictions are very weakly dependent on the details of the model, like the incident FUV radiation field, and the gas density in the disk. Based on this model, we predict a gaseous HDO/H2O ratio in DM Tau of ~1%. In addition, we predict the ground state transition of water at 557 GHz to be undetectable with ODIN and/or HSO-HIFI.

C. Dominik; C. Ceccarelli; D. Hollenbach; M. Kaufman

2005-10-21

392

Development of a gas-phase oxygen biosensor using a blue copper-containing oxidase.  

PubMed

A gas-phase oxygen biosensor based on blue copper-containing oxidases was developed. Blue-oxidase enzymes, including laccase and ascorbate oxidase, have a blue chromophore prosthetic group, type 1 Cu+2, which can be reduced and decolorized with reducing substrates. When the enzyme is reoxidized with molecular oxygen, there is a concomitant return of the blue color. The oxygen biosensor consisted of the Rhus vernicifera laccase and ascorbate as substrate enclosed in pouches of low-density polyethylene under nitrogen gas. Operational stability of the biosensor was established by exposing it to different oxygen/nitrogen gas mixtures at 5 degrees C. Gas-phase oxygen concentrations were measured by keeping it under nitrogen gas and subsequently recording the rate of reappearance of the enzyme blue color, both visually and spectrophotometrically at 610 nm. The oxygen biosensor was able to detect a wide range of oxygen concentrations. The time required to recover the blue color, namely the biosensor response time, at the optimized assay conditions of 5 degrees C and a high-water activity level, was determined. This research describes the development of an oxygen biosensor with adequate activity and stability to measure gas-phase oxygen concentrations at 5 degrees C and high-water activity levels. The oxygen biosensor could be used to indicate oxygen concentrations above acceptable levels in headspace oxygen concentration which could affect the quality and safety of products packaged under initial low levels of oxygen concentration. PMID:8882002

Gardiol, A E; Hernandez, R J; Reinhammar, B; Harte, B R

1996-04-01

393

Liquid-gas Phase Transition in Strange Hadronic Matter with Weak Y-Y Interaction  

E-print Network

The liquid-gas phase transition in strange hadronic matter is reexamined by using the new parameters about the $\\Lambda - \\Lambda$ interaction deduced from recent observation of $^{6}_{\\Lambda\\Lambda}He$ double hypernucleus. The extended Furnstahl-Serot-Tang model with nucleons and hyperons is utilized. The binodal surface, the limit pressure, the entropy, the specific heat capacity and the Caloric curves are addressed. We find that the liquid-gas phase transition can occur more easily in strange hadronic matter with weak Y-Y interaction than that of the strong Y-Y interaction.

Li Yang; Shao Yu Yin; Wei Liang Qian; Ru-keng Su

2005-06-19

394

Density functional molecular computations on protonated serotonin in the gas phase and various solvent media  

NASA Astrophysics Data System (ADS)

5-Hydroxytryptamine (serotonin) was geometry optimized at the B3YP/6-31G(d) level of theory to determine the energetically most favourable conformations of the aromatic hydroxyl group and the protonated ethylamine side chain. The hydroxyl group was found to be most stable at anti for all conformations, and the two lowest energy gas phase conformers found were: ?2= g+, ?3= g- and ?2= g-, ?3= g+. The protonated amino group was found equally stable at g+, g- and anti. The transition structures linking each gas phase minimum were also computed. Minima found were subjected to solvation calculations in chloroform, DMSO, ethanol and water, which shifted their relative stabilities.

Pisterzi, Luca F.; Almeida, David R. P.; Chass, Gregory A.; Torday, Ladislaus L.; Papp, Julius Gy; Varro, Andras; Csizmadia, Imre G.

2002-11-01

395

Study of Hind Limb Tissue Gas Phase Formation in Response to Suspended Adynamia and Hypokinesia  

NASA Technical Reports Server (NTRS)

The purpose of this study was to investigate the hypothesis that reduced joint/muscle activity (hypo kinesia) as well as reduced or null loading of limbs (adynamia) in gravity would result in reduced decompression-induced gas phase and symptoms of decompression sickness (DCS). Finding a correlation between the two phenomena would correspond to the proposed reduction in tissue gas phase formation in astronauts undergoing decompression during extravehicular activity (EVA) in microgravity. The observation may further explain the reported low incidence of DCS in space.

Butler, Bruce D.

1996-01-01

396

Characterization of annular two-phase gas-liquid flows in microgravity  

NASA Technical Reports Server (NTRS)

A series of two-phase gas-liquid flow experiments were developed to study annular flows in microgravity using the NASA Lewis Learjet. A test section was built to measure the liquid film thickness around the perimeter of the tube permitting the three dimensional nature of the gas-liquid interface to be observed. A second test section was used to measure the film thickness, pressure drop and wall shear stress in annular microgravity two-phase flows. Three liquids were studied to determine the effects of liquid viscosity and surface tension. The result of this study provide insight into the wave characteristics, pressure drop and droplet entrainment in microgravity annular flows.

Bousman, W. Scott; Mcquillen, John B.

1994-01-01

397

Thermodynamic analysis of the gas phase composition over uranium-plutonium carbonitride irradiated with fast neutrons  

Microsoft Academic Search

A thermodynamic analysis of the gas phase composition over uranium-plutonium carbonitride U0.8Pu0.2(C0.5N0.5)0.995 irradiated with fast neutrons was carried out with respect to temperature and burnout. In the temperature range of 900–2500\\u000a K, accumulation of fission products in fuel resulted in the formation of a multicomponent gas phase containing the following\\u000a basic elements and compounds: volatile (Cs, Sr, Ba, Se, Te,

G. S. Bulatov; K. N. Gedgovd; D. Yu. Lyubimov

2009-01-01

398

Impact of gas-phase mechanisms on Weather Research Forecasting Model with Chemistry (WRF/Chem) predictions: Mechanism implementation and comparative evaluation  

NASA Astrophysics Data System (ADS)

Gas-phase mechanisms provide important oxidant and gaseous precursors for secondary aerosol formation. Different gas-phase mechanisms may lead to different predictions of gases, aerosols, and aerosol direct and indirect effects. In this study, WRF/Chem-MADRID simulations are conducted over the continental United States for July 2001, with three different gas-phase mechanisms, a default one (i.e., CBM-Z) and two newly implemented ones (i.e., CB05 and SAPRC-99). Simulation results are evaluated against available surface observations, satellite data, and reanalysis data. The model with these three gas-phase mechanisms gives similar predictions of most meteorological variables in terms of spatial distribution and statistics, but large differences exist in shortwave radiation and temperature and relative humidity at 2 m at individual sites under cloudy conditions, indicating the importance of aerosol semi-direct and indirect effects on these variables. Large biases exist in the simulated wind speed at 10 m, cloud water path, cloud optical thickness, and precipitation, due to uncertainties in current cloud microphysics and surface layer parameterizations. Simulations with all three gas-phase mechanisms well reproduce surface concentrations of O3, CO, NO2, and PM2.5, and column NO2. Larger biases exist in the surface concentrations of nitrate and organic matter (OM) and in the spatial distribution of column CO, tropospheric ozone residual, and aerosol optical depth, due to uncertainties in primary OM emissions, limitations in model representations of chemical transport, and radiative processes. Different gas-phase mechanisms lead to different predictions of mass concentrations of O3 (up to 5 ppb), PM2.5 (up to 0.5 ?g m-3), secondary inorganic PM2.5 species (up to 1.1 ?g m-3), organic PM (up to 1.8 ?g m-3), and number concentration of PM2.5 (up to 2 × 104 cm-3). Differences in aerosol mass and number concentrations further lead to sizeable differences in simulated cloud condensation nuclei (CCN) and cloud droplet number concentration (CDNC) due to the feedback mechanisms among H2SO4 vapor, PM2.5 number, CCN, and CDNC through gas-phase chemistry, new particle formation via homogeneous nucleation, aerosol growth, and aerosol activation by cloud droplets. This study illustrates the important impact of gas-phase mechanisms on chemical and aerosol predictions, their subsequent effects on meteorological predictions, and a need for an accurate representation of such feedbacks through various atmospheric processes in the model. The online-coupled models that simulate feedbacks between meteorological variables and chemical species may provide more accurate representations of the real atmosphere for regulatory applications and can be applied to simulate chemistry-climate feedbacks over a longer period of time.

Zhang, Yang; Chen, Yaosheng; Sarwar, Golam; Schere, Kenneth

2012-01-01

399

A numerical method for gas–solid two-phase free turbulent flow using a vortex method  

Microsoft Academic Search

This paper presents a numerical method for gas–solid two-phase free turbulent flow. The computation of the gas flow by a vortex method and the Lagrangian calculation of the particle motion are simultaneously performed, in which the change in the vorticity for the gas-phase by the interaction between the two phases is taken into account. The change due to the force

Tomomi Uchiyama; Masaaki Naruse

2001-01-01

400

Three-phase gas\\/oil\\/brine relative permeabilities measured under CO[sub 2] flooding conditions  

Microsoft Academic Search

Steady-state three-phase gas\\/oil\\/brine relative permeabilities were measured in a carbonate core under CO[sub 2] flooding conditions. Results show that the relative permeability of each phase depends only on the saturation of that phase instead of on two saturations, as many previous studies have concluded. All previously reported gas\\/oil brine relative permeability studies have been conducted with low-pressure N[sub 2] gas

D. E. Dria; G. A. Pope; K. Sepehrnoori

1993-01-01

401

Ab initio and Monte Carlo calculations for a nucleophilic addition reaction in the gas phase and in aqueous solution  

Microsoft Academic Search

Energy profiles for the nucleophilic addition of hydroxide ion to formaldehyde in the gas phase and in aqueous solution have been determined with quantum and statistical mechanical methods. Ab initio calculations at the 6-31+G* level were utilized to study the gas-phase potential energy surface. In the gas phase, the conversion of reactants to the tetrahedral intermediate is exothermic by 35

Jeffry D. Madura; William L. Jorgensen

1986-01-01

402

A microcomputer-controlled gas phase microreactor system  

SciTech Connect

Although automated reactors are effective tools for studying a single type of reaction or optimizing catalyst performance, they may not be well suited for exploratory research. These reactors generally have several shortcomings. First, they may have limited versatility since they are usually designed with a single application in mind. Second, computer systems used for process control and data acquisition are often expensive and complex, so that once they are set up for a given application, it is quite difficult to adapt them for another. Because of these restrictions, experimental reactors are often operated manually, requiring a full-time operator to monitor operations and acquire data. This is a greater problem in laboratories where projects are often short-term, and the costs of setting up an automated reactor may outweigh the benefits of automation. For an automated reactor to be cost-effective in such an environment, both reactor hardware and control software must be versatile enough that they can be easily modified and adapted for different experiments. An automated gas-flow microreactor has been designed and constructed which is both inexpensive and flexible. The reactor is capable of performing three different types of experiments, 1) continuous reagent feed with analysis of the product stream, 2) pulsed-flow experiments, and 3) temperature-programmed desorption (TPD) and reaction (TPR). Conversion of the reactor from one configuration to another requires less than one hour. Process control and data acquisition are performed using an Apple II Plus microcomputer (Apple Computer Corp., Cupertino, Calif.) and an ISAAC interface device (Cyborg Corp., Newton, Mass.).

Morris, R.M.

1983-08-01

403

Parents of two-phase flow and theory of "gas-lift"  

NASA Astrophysics Data System (ADS)

This paper gives a brief overview of types of two-phase flow. Subsequently, it deals with their mutual division and problems with accuracy boundaries among particular types. It also shows the case of water flow through a pipe with external heating and the gradual origination of all kinds of flow. We have met it in solution of safety condition of various stages in pressurized and boiling water reactors. In the MSR there is a problem in the solution of gas-lift using helium as a gas and its secondary usage for clearing of the fuel mixture from gaseous fission products. Theory of gas-lift is described.

Zitek, Pavel; Valenta, Vaclav

2014-03-01

404

Ice Nucleation Activity in Lichens  

PubMed Central

A newly discovered form of biological ice nucleus associated with lichens is described. Ice nucleation spectra of a variety of lichens from the southwestern United States were measured by the drop-freezing method. Several epilithic lichen samples of the genera Rhizoplaca, Xanthoparmelia, and Xanthoria had nuclei active at temperatures as warm as ?2.3°C and had densities of 2.3 × 106 to more than 1 × 108 nuclei g?1 at ?5°C (2 to 4 orders of magnitude higher than any plants infected with ice nucleation-active bacteria). Most lichens tested had nucleation activity above ?8°C. Lichen substrates (rocks, plants, and soil) showed negligible activity above ?8°C. Ice nucleation-active bacteria were not isolated from the lichens, and activity was not destroyed by heat (70°C) or sonication, indicating that lichen-associated ice nuclei are nonbacterial in origin and differ chemically from previously described biological ice nuclei. An axenic culture of the lichen fungus Rhizoplaca chrysoleuca showed detectable ice nucleation activity at ?1.9°C and an ice nucleation density of 4.5 × 106 nuclei g?1 at ?5°C. It is hypothesized that these lichens, which are both frost tolerant and dependent on atmospheric moisture, derive benefit in the form of increased moisture deposition as a result of ice nucleation. PMID:16347678

Kieft, Thomas L.

1988-01-01

405

Gas phase formaldehyde and peroxide measurements in the Arctic atmosphere  

NASA Astrophysics Data System (ADS)

Atmospheric peroxides and formaldehyde were measured during the Polar Sunrise Experiment 1992 in Alert, Canada (82.5°N, 62.3°W). Two measurement periods, in the dark winter and in the sunlit spring, were chosen to investigate the effects of photochemistry. Continuous measurements were performed using diffusion scrubbers coupled to aqueous phase fluorometry. The concentration of total peroxides varied from below the detection limit (~10 parts per trillion by volume (pptv)) to 40 pptv in the dark and 100 to 400 pptv in the sunlit period with large variations in the ratio between H2O2 and organic peroxides. The CH2O concentrations measured in the dark were between 100 and 700 pptv and showed good correlation with a number of atmospheric constituents such as CH4, CO2, and Rn but anticorrelation to O3. A fraction of the observed CH2O concentrations is believed to be formed by nonphotochemical O3-alkene chemistry. In the presence of sunlight the CH2O concentrations ranged between 30 to 600 pptv without correlation to CH4, CO2, or Rn. The maximum CH2O concentrations were associated with air, depleted in O3, coming from the Arctic Ocean. During the O3 depletions, decreased peroxide concentrations were observed. The origin of the air mass was a very important factor during both periods in explaining the observed variabilities in CH2O and peroxide concentrations.

de Serves, Claes

1994-12-01

406

Determination of volatile compounds in grape distillates by solid-phase extraction and gas chromatography  

Microsoft Academic Search

Solid-phase extraction (SPE) procedure on octadecylsilica (C18) was developed for accumulation of volatile compounds from grape distillates. The procedure was optimised for final analysis by capillary gas chromatography. At mass concentrations in model solutions ranging from 0.1 to 50mg\\/l solid-phase extraction recoveries of all analytes ranged from 69% for 2-phenylethanol to 102% for capric acid, with RSD values from 2

Igor Luki?; Mara Banovi?; ?ordano Peršuri?; Sanja Radeka; Barbara Sladonja

2006-01-01

407

Proteomic investigation of natural killer cell microsomes using gas-phase fractionation by mass spectrometry  

Microsoft Academic Search

We have explored the utility of gas-phase fractionation by mass spectrometry (MS) in the mass-to-charge (m\\/z) dimension (GPFm\\/z) for increasing the effective number of protein identifications in cases where sample quantity limits the use of multi-dimensional chromatographic fractionation. A peptide digestate from proteins isolated from the membrane fraction of natural killer (NK) cells was analyzed by microcapillary reversed-phase liquid chromatography

Josip Blonder; Maria Cecilia Rodriguez-Galan; David A. Lucas; Howard A. Young; Haleem J. Issaq; Timothy D. Veenstra; Thomas P. Conrads

2004-01-01

408

Fluorometric method for the determination of gas-phase hydrogen peroxide  

Microsoft Academic Search

The fluorometric gas-phase hydrogen peroxide procedure is based on the technique used by Lazrus et. al. for the determination of H2O2 in the liquid phase. The analytical method utilizes the reaction of H2O2 with horseradish peroxidase and p-hydroxphenylacetic acid (POPHA) to form the fluorescent dimer of POPHA. The analytical reaction responds stoichiometrically to both H2O2 and some organic hydroperoxides. To

Gregory L. Kok; Allan L. Lazrus

1986-01-01

409

Gas-liquid phase-transfer catalysis; A new continuous-flow method in organic synthesis  

Microsoft Academic Search

A synthetic method, gas-liquid phase-transfer catalysis (GL-PTC0), is described. GL-PTC is a continuous-flow procedure where gaseous reagents flow through a molten phase-transfer (PT) catalyst supported on a solid; no solvent is used. Reactions may develop through new mechanistic pathways compared with those of classical conditions; moreover, the reactions often occur in very selective ways. Some typical syntheses carried out under

Pietro Tundo; Giovanni Moraglio; Francesco Trotta

1989-01-01

410

Multifragmentation and nuclear phase transitions (liquid-fog and liquid-gas)  

E-print Network

Thermal multifragmentation of hot nuclei is interpreted as the nuclear liquid-fog phase transition. The charge distributions of the intermediate mass fragments produced in p(3.6 GeV) + Au and p(8.1 GeV) + Au collisions are analyzed within the statistical multifragmentation model with the critical temperature for the nuclear liquid-gas phase transition Tc as a free parameter. The analysis presented here provides strong support for a value of Tc > 15 MeV.

V. A. Karnaukhov; H. Oeschler; S. P. Avdeyev; V. K. Rodionov; A. V. Simomenko; V. V. Kirakosyan; A. Budzanowski; W. Karcz; I. Skwirczynska; E. A. Kuzmin; E. Norbeck; A. S. Botvina

2003-10-10

411

Gas-Phase OH Oxidation of Monoterpenes: Gaseous and Particulate Products  

Microsoft Academic Search

Smog chamber experiments have beenconducted in which cyclic monoterpenes were oxidisedin the gas phase by OH. The evolved secondary organicaerosol (SOA) was analysed by LC-MSn and thegas-phase products were analysed by FT-IR. Theconcentrations of the identified compoundscorresponded to carbon mass balances in the range of40%–90%. The identified compounds in the particularphase corresponded to 0.5%–4.2% of the reactedcarbon. The most abundant

Bo. R. Larsen; Dario Di Bella; Marianne Glasius; Richard Winterhalter; Niels R. Jensen; Jens Hjorth

2001-01-01

412

Climate Impacts of Ice Nucleation  

NASA Technical Reports Server (NTRS)

Several different ice nucleation parameterizations in two different General Circulation Models (GCMs) are used to understand the effects of ice nucleation on the mean climate state, and the Aerosol Indirect Effects (AIE) of cirrus clouds on climate. Simulations have a range of ice microphysical states that are consistent with the spread of observations, but many simulations have higher present-day ice crystal number concentrations than in-situ observations. These different states result from different parameterizations of ice cloud nucleation processes, and feature different balances of homogeneous and heterogeneous nucleation. Black carbon aerosols have a small (0.06 Wm(exp-2) and not statistically significant AIE when included as ice nuclei, for nucleation efficiencies within the range of laboratory measurements. Indirect effects of anthropogenic aerosols on cirrus clouds occur as a consequence of increasing anthropogenic sulfur emissions with different mechanisms important in different models. In one model this is due to increases in homogeneous nucleation fraction, and in the other due to increases in heterogeneous nucleation with coated dust. The magnitude of the effect is the same however. The resulting ice AIE does not seem strongly dependent on the balance between homogeneous and heterogeneous ice nucleation. Regional effects can reach several Wm2. Indirect effects are slightly larger for those states with less homogeneous nucleation and lower ice number concentration in the base state. The total ice AIE is estimated at 0.27 +/- 0.10 Wm(exp-2) (1 sigma uncertainty). This represents a 20% offset of the simulated total shortwave AIE for ice and liquid clouds of 1.6 Wm(sup-2).

Gettelman, Andrew; Liu, Xiaohong; Barahona, Donifan; Lohmann, Ulrike; Chen, Celia

2012-01-01

413

Direct Imaging of the Spatial and Energy Distribution of Nucleation Centers in Ferroelectric Materials  

SciTech Connect

Macroscopic ferroelectric polarization switching, similar to other first order phase transitions, is controlled by nucleation centers. Despite 50 years of extensive theoretical and experimental effort, the microstructural origins of the Landauer paradox, i.e. the experimentally observed low values of coercive fields in ferroelectrics corresponding to implausibly large nucleation activation energies, are still a mystery. In this letter, we develop an approach to visualize the nucleation centers controlling polarization switching processes with nanometer resolution, determine their spatial and energy distribution, and correlate them to local microstructure. The random bond and random field components of the disorder potential are extracted from positive and negative nucleation biases. Observation of enhanced nucleation activity at the 90 domain wall boundaries and intersections combined with phase-field modeling identifies them as a class of nucleation centers that control switching in structural-defect free materials.

Jesse, Stephen [ORNL; Rodriguez, Brian J [ORNL; Choudhury, S [Pennsylvania State University; Baddorf, Arthur P [ORNL; Vrejoiu, I. [Max-Planck-Institut fur Mikrostrukturphysik, Germany; Hesse, D. [Max Planck Institute of Microstructure Physics; Alexe, M. [Max-Planck-Institut fur Mikrostrukturphysik, Germany; Eliseev, E. A. [National Academy of Science of Ukraine, Kiev, Ukraine; Morozovska, A. N. [National Academy of Science of Ukraine, Kiev, Ukraine; Zhang, J [Pennsylvania State University; Chen, L. Q. [Pennsylvania State University; Kalinin, Sergei V [ORNL

2008-01-01

414

Direct imaging of the spatial and energy distribution of nucleation centres in ferroelectric materials.  

PubMed

Macroscopic ferroelectric polarization switching, similar to other first-order phase transitions, is controlled by nucleation centres. Despite 50 years of extensive theoretical and experimental effort, the microstructural origins of the Landauer paradox, that is, the experimentally observed low values of coercive fields in ferroelectrics corresponding to implausibly large nucleation activation energies, are still a mystery. Here, we develop an approach to visualize the nucleation centres controlling polarization switching processes with nanometre resolution, determine their spatial and energy distribution and correlate them to local microstructure. The random-bond and random-field components of the disorder potential are extracted from positive and negative nucleation biases. Observation of enhanced nucleation activity at the 90 composite function domain wall boundaries and intersections combined with phase-field modelling identifies them as a class of nucleation centres that control switching in structural-defect-free materials. PMID:18246074

Jesse, Stephen; Rodriguez, Brian J; Choudhury, Samrat; Baddorf, Arthur P; Vrejoiu, Ionela; Hesse, Dietrich; Alexe, Marin; Eliseev, Eugene A; Morozovska, Anna N; Zhang, Jingxian; Chen, Long-Qing; Kalinin, Sergei V

2008-03-01

415

Nucleation and growth of polycrystalline SiC  

NASA Astrophysics Data System (ADS)

The nucleation and bulk growth of polycrystalline SiC in a 2 inch PVT setup using isostatic and pyrolytic graphite as substrates was studied. Textured nucleation occurs under near-thermal equilibrium conditions at the initial growth stage with hexagonal platelet shaped crystallites of 4H, 6H and 15R polytypes. It is found that pyrolytic graphite results in enhanced texturing of the nucleating gas species. Reducing the pressure leads to growth of the crystallites until a closed polycrystalline SiC layer containing voids with a rough surface is developed. Bulk growth was conducted at 35 mbar Ar pressure at 2250°C in diffusion limited mass transport regime generating a convex shaped growth form of the solid-gas interface leading to lateral expansion of virtually [001] oriented crystallites. Growth at 2350°C led to the stabilization of 6H polytypic grains. The micropipe density in the bulk strongly depends on the substrate used.

Kaiser, M.; Schimmel, S.; Jokubavicius, V.; Linnarsson, M. K.; Ou, H.; Syväjärvi, M.; Wellmann, P.

2014-03-01

416

Flow field simulation of gas-water two phase flow in annular channel  

NASA Astrophysics Data System (ADS)

The gas-water two-phase flow is very common in the industrial processes. the deep understanding of the two-phase flow state is to achieve the production equipment design and safe operation. In the measurement of gas-water two-phase flow, the differential pressure sensor is widely used, and some measurement model of multiphase flow have been concluded. The differential pressure is generated when fluid flowing through the throttling components to calculate flow rate. This paper mainly focuses on two points: 1. The change rule of the parameters include velocity, pressure, phase fraction as the change of time, when the phase inlet velocity is given. 2. Analysis the distribution of the parameters above-mentioned at a certain moment under the condition of different water inlet velocity. Three-dimensional computational fluid dynamics (CFD) approach was used to simulate gas-water two-phase flow fluid in the annular channel, which is composed of horizontal pipe and long- waist cone sensor. The simulation results were obtained from FLUENT software.

Ji, Pengcheng; Dong, Feng

2014-04-01

417

Studies of cluster-assembled materials: From gas phase to condensed phase  

NASA Astrophysics Data System (ADS)

Clusters, defined as "a number of similar things that occur together" in Webster's dictionary, has different meanings depending on the given subject. To physicists and chemists, the word cluster means "a group of atoms or molecules formed by interactions ranging from very weak van der Waals interactions to strong ionic bonds." Unlike molecules, which are made by nature and are stable under ambient conditions, clusters discovered in a laboratory are often metastable. Molecules have specific stoichiometry, whereas the cluster's composition can usually be altered atom by atom. Thus, clusters can be taken as intrinsically "artificial molecules" with considerably more tunabilities in their properties. Research into the relative stability and instability of clusters has in recent years become a very active research area, especially following the study by Khanna and Castleman that first suggested that by varying size and composition, clusters can expand the periodic table to the 3 rd-dimension; that is, clusters can mimic the chemistry of atoms and may, therefore, be used as the building blocks of new materials. The discovery of Met-Cars has drawn worldwide interests and has been actively investigated by researchers from a variety of fields, including physics, chemistry and material science. However, the unsuccessful search for a solvent capable of isolating Met-Cars has impeded progress in characterizing the material in the condensed state and, hence, limited its potential applications as a novel nanoscale material. An alternative method involving the deposition of mass-gated species and the subsequent structural investigation via Transmission Electron Microscopy (TEM) has been employed. With particularly interesting results, soft-landed deposits of zirconium Met-Cars were found to form a face-centered-cubic (FCC) structure with a lattice parameter ˜ 15A. The production of Met-Cars is conducted with the direct laser vaporization (DLV) of metal/graphite composite pellets. After being mass gated in a reflectron equipped time-of-flight mass spectrometer (TOF-MS) and deposited onto TEM grids, the resultant specimens can be loaded onto high-resolution TEM investigation via electron diffraction. In conclusion, soft-landing of mass selected clusters has been shown to be a successful approach to obtain structural information on Zr-Met-Car cluster-assembled materials collected from the gas phase. TEM images indicate the richness of the morphologies associated with these cluster crystals. However, passivation methods are expected to be examined further to overcome the limited stabilities of these novel clusters. From this initial study, it's shown the promising opportunity to study other Met-Cars species and more cluster-based materials. Experimental results of reactions run with a solvothermal synthesis method obtained while searching for new Zr-C cluster assembled materials, are reported. One unexpected product in single crystal form was isolated and tentatively identified by X-ray diffraction to be [Zr6i O(OH)O12·2(Bu)4], with space group P2 1/n and lattice parameters of a = 12.44 A, b = 22.06 A, c = 18.40 A, alpha = 90°, beta = 105°, gamma = 90°, V = 4875 A3 and R 1 = 3.15% for the total observed data (I ? 2 sigma I) and oR2 = 2.82%. This novel hexanuclear Zr(IV)-oxo-hydroxide cluster anion may be the first member in polyoxometalates class with metal atoms from the IVB group and having Oh symmetry. Alternatively, it may be the first member in {[(Zr6Z)X 12]X6}m- class with halides replaced by oxo- and hydroxyl groups and with an increased oxidation state of Zr. It is predicted to bear application potentials directed by both families. This work could suggest a direction in which the preparation of Zr-C cluster-assembled materials in a liquid environment may be eventually fulfilled. 1,3-Bis(diethylphosphino)propane (depp) protected small gold clusters are studied via multiple techniques, including Electrospray Ionization Mass Spectrometry (ESI-MS), Ultraviolet-Visible Spectroscopy (Uv-Vis), Nuclear

Gao, Lin

418

Quantitative Fourier transform infrared analysis of gas phase cigarette smoke and other gas mixtures  

SciTech Connect

A new method for the analysis of selected components in complex gas mixtures has been developed utilizing a relatively inexpensive Fourier transform infrared spectrometer and a continuous flow gas cell. The method was used to monitor nitric oxide and nitrogen dioxide concentrations in cigarette smoke with time. Using multivariate least-square regression analysis, it is possible to simultaneously quantitate both NO and NO{sub 2}, even in the presence of overlapping peaks. Using this method, the oxidation of nitric oxide in the presence of isoprene in cigarette smoke and in a model system was followed with time. The method also can be applied to other compounds in smoke or to any other gaseous mixture.

Cueto, R.; Church, D.F.; Pryor, W.A. (Louisiana State Univ., Baton Rouge (USA))

1989-03-01

419

Steady-state nucleation rate and flux of composite nucleus at saddle point.  

PubMed

The steady-state nucleation rate and flux of composite nucleus at the saddle point is studied by extending the theory of binary nucleation. The Fokker-Planck equation that describes the nucleation flux is derived using the Master equation for the growth of the composite nucleus, which consists of the core of the final stable phase surrounded by a wetting layer of the intermediate metastable phase nucleated from a metastable parent phase recently evaluated by Iwamatsu [J. Chem. Phys. 134, 164508 (2011)]. The Fokker-Planck equation is similar to that used in the theory of binary nucleation, but the non-diagonal elements exist in the reaction rate matrix. First, the general solution for the steady-state nucleation rate and the direction of nucleation flux is derived. Next, this information is then used to study the nucleation of composite nucleus at the saddle point. The dependence of steady-state nucleation rate as well as the direction of nucleation flux on the reaction rate in addition to the free-energy surface is studied using a model free-energy surface. The direction of nucleation current deviates from the steepest-descent direction of the free-energy surface. The results show the importance of two reaction rate constants: one from the metastable environment to the intermediate metastable phase and the other from the metastable intermediate phase to the stable new phase. On the other hand, the gradient of the potential ? or the Kramers crossover function (the commitment or splitting probability) is relatively insensitive to reaction rates or free-energy surface. PMID:22667576

Iwamatsu, Masao

2012-05-28

420

Steady-state nucleation rate and flux of composite nucleus at saddle point  

NASA Astrophysics Data System (ADS)

The steady-state nucleation rate and flux of composite nucleus at the saddle point is studied by extending the theory of binary nucleation. The Fokker-Planck equation that describes the nucleation flux is derived using the Master equation for the growth of the composite nucleus, which consists of the core of the final stable phase surrounded by a wetting layer of the intermediate metastable phase nucleated from a metastable parent phase recently evaluated by Iwamatsu [J. Chem. Phys. 134, 164508 (2011)]. The Fokker-Planck equation is similar to that used in the theory of binary nucleation, but the non-diagonal elements exist in the reaction rate matrix. First, the general solution for the steady-state nucleation rate and the direction of nucleation flux is derived. Next, this information is then used to study the nucleation of composite nucleus at the saddle point. The dependence of steady-state nucleation rate as well as the direction of nucleation flux on the reaction rate in addition to the free-energy surface is studied using a model free-energy surface. The direction of nucleation current deviates from the steepest-descent direction of the free-energy surface. The results show the importance of two reaction rate constants: one from the metastable environment to the intermediate metastable phase and the other from the metastable intermediate phase to the stable new phase. On the other hand, the gradient of the potential ? or the Kramers crossover function (the commitment or splitting probability) is relatively insensitive to reaction rates or free-energy surface.

Iwamatsu, Masao

2012-05-01